diff --git a/package.json b/package.json
index b00f0ce..aedd772 100644
--- a/package.json
+++ b/package.json
@@ -14,7 +14,7 @@
     "d3-selection": "^3.0.0",
     "d3-shape": "^3.2.0",
     "powerbi-visuals-api": "~3.6.0",
-    "powerbi-visuals-utils-dataviewutils": "^2.2.1"
+    "powerbi-visuals-utils-dataviewutils": "^6.0.1"
   },
   "devDependencies": {
     "@types/d3-array": "^3.0.5",
@@ -22,13 +22,12 @@
     "@types/d3-scale": "^4.0.3",
     "@types/d3-selection": "^3.0.5",
     "@types/d3-shape": "^3.1.1",
-    "@typescript-eslint/eslint-plugin": "^5.59.8",
-    "@typescript-eslint/parser": "^5.59.8",
-    "eslint": "^8.41.0",
+    "@typescript-eslint/eslint-plugin": "^6.2.0",
+    "@typescript-eslint/parser": "^6.2.0",
+    "eslint": "^8.45.0",
     "eslint-plugin-powerbi-visuals": "^0.8.1",
-    "process": "^0.11.10",
-    "ts-loader": "9.4.2",
-    "typescript": "3.6.3"
+    "ts-loader": "9.4.4",
+    "typescript": "5.1.6"
   },
   "override": {
     "powerbi-visuals-api": "$powerbi-visuals-api"
diff --git a/src/Classes/controlLimitsClass.ts b/src/Classes/controlLimitsClass.ts
index a040ad0..b5c349e 100644
--- a/src/Classes/controlLimitsClass.ts
+++ b/src/Classes/controlLimitsClass.ts
@@ -8,13 +8,14 @@ import checkFlagDirection from "../Functions/checkFlagDirection"
 import truncate from "../Functions/truncate";
 import { truncateInputs } from "../Functions/truncate";
 import { multiply } from "../Functions/BinaryFunctions";
+import isNotNullOrUndefined from "../Functions/isNotNullOrUndefined";
 
 type controlLimitsArgs = {
   inputSettings: settingsClass,
   keys: { x: number, id: number, label: string }[];
   values: number[];
-  numerators?: number[];
-  denominators?: number[];
+  numerators?: number[] | undefined;
+  denominators?: number[] | undefined;
   targets: number[];
   ll99: number[];
   ll95: number[];
@@ -30,7 +31,7 @@ export default class controlLimitsClass {
   numerators?: number[];
   denominators?: number[];
   targets: number[];
-  alt_targets?: number[];
+  alt_targets: number[];
   ll99: number[];
   ll95: number[];
   ul95: number[];
@@ -86,30 +87,32 @@ export default class controlLimitsClass {
     }
   }
 
-  constructor(args: controlLimitsArgs) {
-    this.keys = args.keys;
-    this.values = args.values;
-    if (args.numerators || !(args.numerators === null || args.numerators === undefined)) {
-      this.numerators = args.numerators;
-    }
-    if (args.denominators || !(args.denominators === null || args.denominators === undefined)) {
-      this.denominators = args.denominators;
-    }
-    this.targets = args.targets;
-    this.alt_targets = rep(args.inputSettings.spc.alt_target, args.values.length)
-    this.ll99 = args.ll99;
-    this.ll95 = args.ll95;
-    this.ul95 = args.ul95;
-    this.ul99 = args.ul99;
-    this.astpoint = rep("none", args.values.length);
-    this.trend = rep("none", args.values.length);
-    this.two_in_three = rep("none", args.values.length);
-    this.shift = rep("none", args.values.length);
-    if (args.count || !(args.count === null || args.count === undefined)) {
-      this.count = args.count;
-    }
+  constructor(args?: controlLimitsArgs) {
+    if (args) {
+      this.keys = args.keys;
+      this.values = args.values;
+      if (isNotNullOrUndefined(args.numerators)) {
+        this.numerators = args.numerators;
+      }
+      if (isNotNullOrUndefined(args.denominators)) {
+        this.denominators = args.denominators;
+      }
+      this.targets = args.targets;
+      this.alt_targets = rep(args.inputSettings.spc.alt_target, args.values.length)
+      this.ll99 = args.ll99;
+      this.ll95 = args.ll95;
+      this.ul95 = args.ul95;
+      this.ul99 = args.ul99;
+      this.astpoint = rep("none", args.values.length);
+      this.trend = rep("none", args.values.length);
+      this.two_in_three = rep("none", args.values.length);
+      this.shift = rep("none", args.values.length);
+      if (args.count || !(args.count === null || args.count === undefined)) {
+        this.count = args.count;
+      }
 
-    this.scaleAndTruncateLimits(args.inputSettings)
-    this.flagOutliers(args.inputSettings)
+      this.scaleAndTruncateLimits(args.inputSettings)
+      this.flagOutliers(args.inputSettings)
+    }
   }
 }
diff --git a/src/Classes/dataClass.ts b/src/Classes/dataClass.ts
index 1cd7ae1..bd055a9 100644
--- a/src/Classes/dataClass.ts
+++ b/src/Classes/dataClass.ts
@@ -22,44 +22,48 @@ export default class dataClass {
   scatter_formatting: defaultSettingsType["scatter"][];
   tooltips: VisualTooltipDataItem[][];
 
-  constructor(inputView: DataViewCategorical, inputSettings: settingsClass) {
-    const numerators: number[] = extractDataColumn<number[]>(inputView, "numerators", inputSettings);
-    const denominators: number[] = extractDataColumn<number[]>(inputView, "denominators", inputSettings);
-    const xbar_sds: number[] = extractDataColumn<number[]>(inputView, "xbar_sds", inputSettings);
-    const keys: string[] = extractDataColumn<string[]>(inputView, "key", inputSettings);
-    const scatter_cond = extractConditionalFormatting(inputView, "scatter", inputSettings) as defaultSettingsType["scatter"][];
-    const tooltips = extractDataColumn<VisualTooltipDataItem[][]>(inputView, "tooltips", inputSettings);
+  constructor(inputView?: DataViewCategorical, inputSettings?: settingsClass) {
+    if (inputView && inputSettings) {
+      const numerators: number[] = extractDataColumn<number[]>(inputView, "numerators", inputSettings);
+      const denominators: number[] = extractDataColumn<number[]>(inputView, "denominators", inputSettings);
+      const xbar_sds: number[] = extractDataColumn<number[]>(inputView, "xbar_sds", inputSettings);
+      const keys: string[] = extractDataColumn<string[]>(inputView, "key", inputSettings);
+      const scatter_cond = extractConditionalFormatting(inputView, "scatter", inputSettings) as defaultSettingsType["scatter"][];
+      const tooltips = extractDataColumn<VisualTooltipDataItem[][]>(inputView, "tooltips", inputSettings);
 
-    const valid_ids: number[] = new Array<number>();
-    const valid_keys: { x: number, id: number, label: string }[] = new Array<{ x: number, id: number, label: string }>();
+      const valid_ids: number[] = new Array<number>();
+      const valid_keys: { x: number, id: number, label: string }[] = new Array<{ x: number, id: number, label: string }>();
 
-    for (let i: number = 0; i < numerators.length; i++) {
-      if (checkValidInput(numerators[i],
-                          denominators ? denominators[i] : null,
-                          xbar_sds ? xbar_sds[i] : null, inputSettings.spc.chart_type)) {
-        valid_ids.push(i);
-        valid_keys.push({ x: null, id: i, label: keys[i] })
+      let validCount: number = 0
+      for (let i: number = 0; i < numerators.length; i++) {
+        if (checkValidInput(numerators[i],
+                            denominators ? denominators[i] : null,
+                            xbar_sds ? xbar_sds[i] : null, inputSettings.spc.chart_type)) {
+          valid_ids.push(i);
+          valid_keys.push({ x: validCount, id: i, label: keys[i] })
+          validCount += 1;
+        }
+      }
+
+      let percent_labels: boolean;
+      if (inputSettings.spc.perc_labels === "Automatic") {
+        percent_labels = ["p", "pp"].includes(inputSettings.spc.chart_type) && (inputSettings.spc.multiplier === 1 || inputSettings.spc.multiplier === 100);
+      } else {
+        percent_labels = inputSettings.spc.perc_labels === "Yes";
       }
-    }
 
-    valid_keys.forEach((d, idx) => { d.x = idx });
+      const inputValues = (inputView.values as powerbi.DataViewValueColumns)[0];
 
-    let percent_labels: boolean;
-    if (inputSettings.spc.perc_labels === "Automatic") {
-      percent_labels = ["p", "pp"].includes(inputSettings.spc.chart_type) && (inputSettings.spc.multiplier === 1 || inputSettings.spc.multiplier === 100);
-    } else {
-      percent_labels = inputSettings.spc.perc_labels === "Yes";
+      this.keys = valid_keys;
+      this.numerators = extractValues(numerators, valid_ids);
+      this.denominators = extractValues(denominators, valid_ids);
+      this.xbar_sds = extractValues(xbar_sds, valid_ids);
+      this.tooltips = extractValues(tooltips, valid_ids);
+      this.highlights = inputValues.highlights ? extractValues(inputValues.highlights, valid_ids) : new Array<PrimitiveValue>;
+      this.anyHighlights = (this.highlights.length > 0)
+      this.categories = (inputView.categories as powerbi.DataViewCategoryColumn[])[0];
+      this.percentLabels = percent_labels;
+      this.scatter_formatting = extractValues(scatter_cond, valid_ids);
     }
-
-    this.keys = valid_keys;
-    this.numerators = extractValues(numerators, valid_ids);
-    this.denominators = extractValues(denominators, valid_ids);
-    this.xbar_sds = extractValues(xbar_sds, valid_ids);
-    this.tooltips = extractValues(tooltips, valid_ids);
-    this.highlights = inputView.values[0].highlights ? extractValues(inputView.values[0].highlights, valid_ids) : inputView.values[0].highlights;
-    this.anyHighlights = this.highlights ? true : false
-    this.categories = inputView.categories[0];
-    this.percentLabels = percent_labels;
-    this.scatter_formatting = extractValues(scatter_cond, valid_ids);
   }
 }
diff --git a/src/Classes/plotPropertiesClass.ts b/src/Classes/plotPropertiesClass.ts
index 0409205..2b7bacb 100644
--- a/src/Classes/plotPropertiesClass.ts
+++ b/src/Classes/plotPropertiesClass.ts
@@ -6,6 +6,7 @@ import { plotData } from "./viewModelClass"
 import settingsClass from "./settingsClass";
 import dataClass from "./dataClass";
 import controlLimitsClass from "./controlLimitsClass";
+import isNotNullOrUndefined from "../Functions/isNotNullOrUndefined";
 
 export type axisProperties = {
   lower: number,
@@ -52,7 +53,8 @@ export default class plotPropertiesClass {
                       plotPoints: plotData[],
                       controlLimits: controlLimitsClass,
                       inputData: dataClass,
-                      inputSettings: settingsClass }): void {
+                      inputSettings: settingsClass,
+                    invalidDataView: boolean }): void {
 
     // Get the width and height of plotting space
     this.width = args.options.viewport.width;
@@ -60,7 +62,7 @@ export default class plotPropertiesClass {
 
     this.displayPlot = args.plotPoints
       ? args.plotPoints.length > 1
-      : null;
+      : false;
 
     const xLowerLimit: number = args.inputSettings.x_axis.xlimit_l;
     let xUpperLimit: number = args.inputSettings.x_axis.xlimit_u;
@@ -68,8 +70,10 @@ export default class plotPropertiesClass {
     let yUpperLimit: number = args.inputSettings.y_axis.ylimit_u;
 
     // Only update data-/settings-dependent plot aesthetics if they have changed
-    if (args.inputData && args.controlLimits) {
-      xUpperLimit = xUpperLimit !== null ? xUpperLimit : d3.max(args.controlLimits.keys.map(d => d.x))
+    if (!args.invalidDataView) {
+      xUpperLimit = isNotNullOrUndefined(xUpperLimit)
+                      ? xUpperLimit
+                      : d3.max(args.controlLimits.keys.map(d => d.x));
 
       const limitMultiplier: number = args.inputSettings.y_axis.limit_multiplier;
       const chart_type: string = args.inputSettings.spc.chart_type;
@@ -77,10 +81,10 @@ export default class plotPropertiesClass {
       const ul99: number[] = args.controlLimits.ul99;
       const ll99: number[] = args.controlLimits.ll99;
       const alt_targets: number[] = args.controlLimits.alt_targets;
-      const maxValueOrLimit: number = d3.max(values.concat(ul99).concat(alt_targets));
-      const minValueOrLimit: number = d3.min(values.concat(ll99).concat(alt_targets));
-      const maxTarget: number = d3.max(args.controlLimits.targets);
-      const minTarget: number = d3.min(args.controlLimits.targets);
+      const maxValueOrLimit: number = d3.max((values.concat(ul99).concat(alt_targets)));
+      const minValueOrLimit: number = d3.min((values.concat(ll99).concat(alt_targets)));
+      const maxTarget: number = d3.max((args.controlLimits.targets));
+      const minTarget: number = d3.min((args.controlLimits.targets));
 
       const upperLimitRaw: number = maxTarget + (maxValueOrLimit - maxTarget) * limitMultiplier;
       const lowerLimitRaw: number = minTarget - (minTarget - minValueOrLimit) * limitMultiplier;
diff --git a/src/Classes/settingsClass.ts b/src/Classes/settingsClass.ts
index 625ea6a..31ffa42 100644
--- a/src/Classes/settingsClass.ts
+++ b/src/Classes/settingsClass.ts
@@ -1,6 +1,5 @@
 import powerbi from "powerbi-visuals-api";
 import DataView = powerbi.DataView;
-import DataViewCategorical = powerbi.DataViewCategorical;
 import DataViewPropertyValue = powerbi.DataViewPropertyValue
 import VisualObjectInstanceEnumerationObject = powerbi.VisualObjectInstanceEnumerationObject;
 import VisualEnumerationInstanceKinds = powerbi.VisualEnumerationInstanceKinds;
@@ -10,6 +9,7 @@ import { dataViewWildcard } from "powerbi-visuals-utils-dataviewutils";
 import extractConditionalFormatting from "../Functions/extractConditionalFormatting";
 import defaultSettings from "../defaultSettings"
 import { defaultSettingsType, defaultSettingsKey, settingsPaneGroupings } from "../defaultSettings";
+import isNotNullOrUndefined from "../Functions/isNotNullOrUndefined";
 
 /**
  * This is the core class which controls the initialisation and
@@ -40,13 +40,19 @@ export default class settingsClass implements defaultSettingsType {
     const allSettingGroups: string[] = Object.getOwnPropertyNames(this);
 
     allSettingGroups.forEach(settingGroup => {
-      const categoricalView: DataViewCategorical = inputView.categorical ? inputView.categorical : null;
-      const condFormatting: defaultSettingsType[defaultSettingsKey] = extractConditionalFormatting(categoricalView, settingGroup, this)[0];
+      let condFormatting: defaultSettingsType[defaultSettingsKey] | undefined;
+      if (isNotNullOrUndefined(inputView.categorical)) {
+        if (isNotNullOrUndefined(inputView.categorical.categories)) {
+          condFormatting = extractConditionalFormatting(inputView.categorical, settingGroup, this)[0];
+        }
+      }
       // Get the names of all settings in a given class and
       // use those to extract and update the relevant values
       const settingNames: string[] = Object.getOwnPropertyNames(this[settingGroup]);
       settingNames.forEach(settingName => {
-        this[settingGroup][settingName] = condFormatting ? condFormatting[settingName] : defaultSettings[settingGroup][settingName]
+        this[settingGroup][settingName] = isNotNullOrUndefined(condFormatting)
+                                            ? (condFormatting as defaultSettingsType[defaultSettingsKey])[settingName]
+                                            : defaultSettings[settingGroup][settingName]
       })
     })
   }
diff --git a/src/Classes/viewModelClass.ts b/src/Classes/viewModelClass.ts
index 4ea024f..ef65dbb 100644
--- a/src/Classes/viewModelClass.ts
+++ b/src/Classes/viewModelClass.ts
@@ -18,7 +18,7 @@ import * as limitFunctions from "../Limit Calculations"
 
 export class lineData {
   x: number;
-  line_value: number;
+  line_value: number | null;
   group: string;
 }
 
@@ -46,23 +46,31 @@ export default class viewModelClass {
   firstRun: boolean;
   limitFunction: (inputData: dataClass, inputSettings: settingsClass) => controlLimitsClass;
 
+  constructor() {
+    this.inputData = new dataClass();
+    this.inputSettings = new settingsClass();
+    this.plotPoints = new Array<plotData>();
+    this.groupedLines = new Array<[string, lineData[]]>();
+    this.plotProperties = new plotPropertiesClass();
+    this.plotProperties.firstRun = true;
+    this.firstRun = true
+    this.splitIndexes = new Array<number>();
+  }
+
   update(options: VisualUpdateOptions, host: IVisualHost) {
-    if (this.firstRun) {
-      this.inputSettings = new settingsClass();
-    }
     const dv: powerbi.DataView[] = options.dataViews;
     this.inputSettings.update(dv[0]);
 
-    const split_indexes_storage: DataViewObject = dv[0].metadata.objects ? dv[0].metadata.objects.split_indexes_storage : null;
-    const split_indexes: DataViewPropertyValue = split_indexes_storage ? split_indexes_storage.split_indexes : null;
+    const split_indexes_storage: DataViewObject | null = dv[0].metadata.objects ? dv[0].metadata.objects.split_indexes_storage : null;
+    const split_indexes: DataViewPropertyValue | null = split_indexes_storage ? split_indexes_storage.split_indexes : null;
     this.splitIndexes = split_indexes ? JSON.parse(<string>(split_indexes)) : new Array<number>();
 
+    const invalidDataView: boolean = checkInvalidDataView(dv);
     // Make sure that the construction returns early with null members so
     // that the visual does not crash when trying to process invalid data
-    if (checkInvalidDataView(dv)) {
-      this.inputData = <dataClass>null;
-      this.limitFunction = null;
-      this.controlLimits = null;
+    if (invalidDataView) {
+      this.inputData = new dataClass();
+      this.controlLimits = new controlLimitsClass();
       this.plotPoints = new Array<plotData>();
       this.groupedLines = new Array<[string, lineData[]]>();
       this.splitIndexes = new Array<number>();
@@ -85,16 +93,13 @@ export default class viewModelClass {
         this.initialiseGroupedLines();
       }
     }
-    if (this.firstRun) {
-      this.plotProperties = new plotPropertiesClass();
-      this.plotProperties.firstRun = true;
-    }
     this.plotProperties.update({
       options: options,
       plotPoints: this.plotPoints,
       controlLimits: this.controlLimits,
       inputData: this.inputData,
-      inputSettings: this.inputSettings
+      inputSettings: this.inputSettings,
+      invalidDataView: invalidDataView
     })
     this.firstRun = false;
   }
@@ -167,7 +172,7 @@ export default class viewModelClass {
                       .withCategory(this.inputData.categories,
                                     this.inputData.keys[i].id)
                       .createSelectionId(),
-        highlighted: this.inputData.highlights ? (this.inputData.highlights[index] ? true : false) : false,
+        highlighted: this.inputData.anyHighlights ? (this.inputData.highlights[index] ? true : false) : false,
         tooltip: buildTooltip(i, this.controlLimits, this.inputData, this.inputSettings)
       })
       this.tickLabels.push({x: index, label: this.controlLimits.keys[i].label});
@@ -200,16 +205,4 @@ export default class viewModelClass {
     }
     this.groupedLines = d3.groups(formattedLines, d => d.group);
   }
-
-  constructor() {
-    this.inputData = <dataClass>null;
-    this.inputSettings = <settingsClass>null;
-    this.limitFunction = null;
-    this.controlLimits = null;
-    this.plotPoints = new Array<plotData>();
-    this.groupedLines = new Array<[string, lineData[]]>();
-    this.plotProperties = <plotPropertiesClass>null;
-    this.firstRun = true
-    this.splitIndexes = new Array<number>();
-  }
 }
diff --git a/src/D3 Plotting Functions/Assurance Icons/consistentFail.ts b/src/D3 Plotting Functions/Assurance Icons/consistentFail.ts
index fde0013..1d327ff 100644
--- a/src/D3 Plotting Functions/Assurance Icons/consistentFail.ts	
+++ b/src/D3 Plotting Functions/Assurance Icons/consistentFail.ts	
@@ -1,4 +1,4 @@
-import { svgBaseType } from "../../visual"
+import { iconSelection } from "../drawIcons"
 
 /**
  * Inline function to be called by D3 for rendering the Assurance - Fail icon.
@@ -9,7 +9,7 @@ import { svgBaseType } from "../../visual"
  *
  * @param selection The D3 parent object to which the icon's SVG code will be added
  */
-export default function consistentFail(selection: svgBaseType): void {
+export default function consistentFail(selection: iconSelection): void {
   selection.append("g")
             .attr("clip-path","url(#clip2)")
             .append("g")
diff --git a/src/D3 Plotting Functions/Assurance Icons/consistentPass.ts b/src/D3 Plotting Functions/Assurance Icons/consistentPass.ts
index ae6e6b3..22ac4b5 100644
--- a/src/D3 Plotting Functions/Assurance Icons/consistentPass.ts	
+++ b/src/D3 Plotting Functions/Assurance Icons/consistentPass.ts	
@@ -1,4 +1,4 @@
-import { svgBaseType } from "../../visual"
+import { iconSelection } from "../drawIcons"
 
 /**
  * Inline function to be called by D3 for rendering the Assurance - Pass icon.
@@ -9,7 +9,7 @@ import { svgBaseType } from "../../visual"
  *
  * @param selection The D3 parent object to which the icon's SVG code will be added
  */
-export default function consistentPass(selection: svgBaseType): void {
+export default function consistentPass(selection: iconSelection): void {
   selection.append("g")
             .attr("clip-path","url(#clip2)")
             .append("g")
diff --git a/src/D3 Plotting Functions/Assurance Icons/inconsistent.ts b/src/D3 Plotting Functions/Assurance Icons/inconsistent.ts
index 3b888b9..c7eb556 100644
--- a/src/D3 Plotting Functions/Assurance Icons/inconsistent.ts	
+++ b/src/D3 Plotting Functions/Assurance Icons/inconsistent.ts	
@@ -1,5 +1,4 @@
-import { svgBaseType } from "../../visual"
-
+import { iconSelection } from "../drawIcons"
 /**
  * Inline function to be called by D3 for rendering the Assurance - Iconsistent icon.
  * The code below is a translation from HTML to D3 syntax of the SVG file:
@@ -9,7 +8,7 @@ import { svgBaseType } from "../../visual"
  *
  * @param selection The D3 parent object to which the icon's SVG code will be added
  */
-export default function inconsistent(selection: svgBaseType): void {
+export default function inconsistent(selection: iconSelection): void {
   selection.append("g")
             .attr("clip-path","url(#clip2)")
             .append("g")
diff --git a/src/D3 Plotting Functions/D3 Modules/index.ts b/src/D3 Plotting Functions/D3 Modules/index.ts
index 047f8bf..1273deb 100644
--- a/src/D3 Plotting Functions/D3 Modules/index.ts	
+++ b/src/D3 Plotting Functions/D3 Modules/index.ts	
@@ -1,5 +1,17 @@
+import { min as d3min, max as d3max, mean as d3mean, median as d3median } from "d3-array";
+
+/**
+ * D3 Array reduction functions have return type number | undefined,
+ * redefine these to remove the 'undefined' as that is handled separately
+ */
+const min = (x: number[]): number => d3min(x) as number;
+const max = (x: number[]): number => d3max(x) as number;
+const mean = (x: number[]): number => d3mean(x) as number;
+const median = (x: number[]): number => d3median(x) as number;
+
 export { select, selectAll, Selection, BaseType } from "d3-selection";
-export { groups, leastIndex, mean, median, sum, max, min } from "d3-array";
+export { groups, leastIndex, sum } from "d3-array";
+export { min, max, mean, median };
 export { line } from "d3-shape"
 export { Axis, axisBottom, axisLeft } from "d3-axis"
 export { ScaleLinear, scaleLinear, NumberValue } from "d3-scale"
diff --git a/src/D3 Plotting Functions/Variation Icons/commonCause.ts b/src/D3 Plotting Functions/Variation Icons/commonCause.ts
index bf6b054..2441b82 100644
--- a/src/D3 Plotting Functions/Variation Icons/commonCause.ts	
+++ b/src/D3 Plotting Functions/Variation Icons/commonCause.ts	
@@ -1,4 +1,4 @@
-import { svgBaseType } from "../../visual";
+import { iconSelection } from "../drawIcons"
 
 /**
  * Inline function to be called by D3 for rendering the Variation - Common Cause icon.
@@ -9,7 +9,7 @@ import { svgBaseType } from "../../visual";
  *
  * @param selection The D3 parent object to which the icon's SVG code will be added
  */
-export default function commonCause(selection: svgBaseType): void {
+export default function commonCause(selection: iconSelection): void {
   selection.append("g")
             .attr("clip-path","url(#clip2)")
             .append("g")
diff --git a/src/D3 Plotting Functions/Variation Icons/concernHigh.ts b/src/D3 Plotting Functions/Variation Icons/concernHigh.ts
index 6c38a28..6d69593 100644
--- a/src/D3 Plotting Functions/Variation Icons/concernHigh.ts	
+++ b/src/D3 Plotting Functions/Variation Icons/concernHigh.ts	
@@ -1,4 +1,4 @@
-import { svgBaseType } from "../../visual";
+import { iconSelection } from "../drawIcons"
 
 /**
  * Inline function to be called by D3 for rendering the Variation - Concern High icon.
@@ -12,7 +12,7 @@ import { svgBaseType } from "../../visual";
 
 // ESLint errors due to number of lines in function, but would reduce readability to separate further
 /* eslint-disable */
-export default function concernHigh(selection: svgBaseType): void {
+export default function concernHigh(selection: iconSelection): void {
   selection.append("g")
             .attr("clip-path","url(#clip2)")
             .append("g")
diff --git a/src/D3 Plotting Functions/Variation Icons/concernLow.ts b/src/D3 Plotting Functions/Variation Icons/concernLow.ts
index bdece3c..f410c09 100644
--- a/src/D3 Plotting Functions/Variation Icons/concernLow.ts	
+++ b/src/D3 Plotting Functions/Variation Icons/concernLow.ts	
@@ -1,4 +1,4 @@
-import { svgBaseType } from "../../visual"
+import { iconSelection } from "../drawIcons"
 
 /**
  * Inline function to be called by D3 for rendering the Variation - Concern Low icon.
@@ -9,7 +9,7 @@ import { svgBaseType } from "../../visual"
  *
  * @param selection The D3 parent object to which the icon's SVG code will be added
  */
-export default function concernLow(selection: svgBaseType): void {
+export default function concernLow(selection: iconSelection): void {
   selection.append("g")
             .attr("clip-path","url(#clip2)")
             .append("g")
diff --git a/src/D3 Plotting Functions/Variation Icons/improvementHigh.ts b/src/D3 Plotting Functions/Variation Icons/improvementHigh.ts
index 2daa0c7..88945ca 100644
--- a/src/D3 Plotting Functions/Variation Icons/improvementHigh.ts	
+++ b/src/D3 Plotting Functions/Variation Icons/improvementHigh.ts	
@@ -1,4 +1,4 @@
-import { svgBaseType } from "../../visual"
+import { iconSelection } from "../drawIcons"
 
 /**
  * Inline function to be called by D3 for rendering the Variation - Improvement High icon.
@@ -12,7 +12,7 @@ import { svgBaseType } from "../../visual"
 
 // ESLint errors due to number of lines in function, but would reduce readability to separate further
 /* eslint-disable */
-export default function improvementHigh(selection: svgBaseType): void {
+export default function improvementHigh(selection: iconSelection): void {
   selection.append("g")
             .attr("clip-path","url(#clip2)")
             .append("g")
diff --git a/src/D3 Plotting Functions/Variation Icons/improvementLow.ts b/src/D3 Plotting Functions/Variation Icons/improvementLow.ts
index 87e288e..6888df9 100644
--- a/src/D3 Plotting Functions/Variation Icons/improvementLow.ts	
+++ b/src/D3 Plotting Functions/Variation Icons/improvementLow.ts	
@@ -1,4 +1,4 @@
-import { svgBaseType } from "../../visual"
+import { iconSelection } from "../drawIcons"
 
 /**
  * Inline function to be called by D3 for rendering the Variation - Improvement Low icon.
@@ -9,7 +9,7 @@ import { svgBaseType } from "../../visual"
  *
  * @param selection The D3 parent object to which the icon's SVG code will be added
  */
-export default function improvementLow(selection: svgBaseType): void {
+export default function improvementLow(selection: iconSelection): void {
   selection.append("g")
             .attr("clip-path","url(#clip2)")
             .append("g")
diff --git a/src/D3 Plotting Functions/Variation Icons/neutralHigh.ts b/src/D3 Plotting Functions/Variation Icons/neutralHigh.ts
index 1ea151e..3ffe560 100644
--- a/src/D3 Plotting Functions/Variation Icons/neutralHigh.ts	
+++ b/src/D3 Plotting Functions/Variation Icons/neutralHigh.ts	
@@ -1,4 +1,4 @@
-import { svgBaseType } from "../../visual"
+import { iconSelection } from "../drawIcons"
 
 /**
  * Inline function to be called by D3 for rendering the Variation - Neutral High icon.
@@ -9,7 +9,7 @@ import { svgBaseType } from "../../visual"
  *
  * @param selection The D3 parent object to which the icon's SVG code will be added
  */
-export default function neutralHigh(selection: svgBaseType): void {
+export default function neutralHigh(selection: iconSelection): void {
   selection.append("g")
             .attr("clip-path","url(#clip2)")
             .append("g")
diff --git a/src/D3 Plotting Functions/Variation Icons/neutralLow.ts b/src/D3 Plotting Functions/Variation Icons/neutralLow.ts
index dba1f5c..ab6ed06 100644
--- a/src/D3 Plotting Functions/Variation Icons/neutralLow.ts	
+++ b/src/D3 Plotting Functions/Variation Icons/neutralLow.ts	
@@ -1,4 +1,4 @@
-import { svgBaseType } from "../../visual"
+import { iconSelection } from "../drawIcons"
 
 /**
  * Inline function to be called by D3 for rendering the Variation - Neutral Low icon.
@@ -9,7 +9,7 @@ import { svgBaseType } from "../../visual"
  *
  * @param selection The D3 parent object to which the icon's SVG code will be added
  */
-export default function neutralLow(selection: svgBaseType): void {
+export default function neutralLow(selection: iconSelection): void {
   selection.append("g")
             .attr("clip-path","url(#clip2)")
             .append("g")
diff --git a/src/D3 Plotting Functions/drawDots.ts b/src/D3 Plotting Functions/drawDots.ts
index 049b7b5..15fd3c3 100644
--- a/src/D3 Plotting Functions/drawDots.ts	
+++ b/src/D3 Plotting Functions/drawDots.ts	
@@ -33,7 +33,7 @@ export default function drawDots(selection: svgBaseType, visualObj: Visual) {
             visualObj.host.persistProperties({
               replace: [{
                 objectName: "split_indexes_storage",
-                selector: undefined,
+                selector: {},
                 properties: { split_indexes: JSON.stringify(visualObj.viewModel.splitIndexes) }
               }]
             });
diff --git a/src/D3 Plotting Functions/drawIcons.ts b/src/D3 Plotting Functions/drawIcons.ts
index 62aba68..6d77a9c 100644
--- a/src/D3 Plotting Functions/drawIcons.ts	
+++ b/src/D3 Plotting Functions/drawIcons.ts	
@@ -1,10 +1,13 @@
 import * as variationIcon from "./Variation Icons"
 import * as assuranceIcon from "./Assurance Icons"
+import * as d3 from "./D3 Modules"
 import variationIconsToDraw from "../Functions/variationIconsToDraw";
 import initialiseIconSVG from "./initialiseIconSVG";
 import { svgBaseType, Visual } from "../visual";
 import assuranceIconToDraw from "../Functions/assuranceIconToDraw";
 
+export type iconSelection = d3.Selection<d3.BaseType, unknown, SVGSVGElement, unknown>;
+
 export default function drawIcons(selection: svgBaseType, visualObj: Visual): void {
   selection.selectAll(".icongroup").remove()
   if (!(visualObj.viewModel.plotProperties.displayPlot)) {
@@ -33,6 +36,7 @@ export default function drawIcons(selection: svgBaseType, visualObj: Visual): vo
     const assurance_location: string = visualObj.viewModel.inputSettings.nhs_icons.assurance_icons_locations;
     const assurance_scaling: number = visualObj.viewModel.inputSettings.nhs_icons.assurance_icons_scaling;
     const assuranceIconPresent: string = assuranceIconToDraw(visualObj.viewModel);
+
     if (assuranceIconPresent === "none") {
       return;
     }
diff --git a/src/D3 Plotting Functions/drawLines.ts b/src/D3 Plotting Functions/drawLines.ts
index a833405..3d1a6cf 100644
--- a/src/D3 Plotting Functions/drawLines.ts	
+++ b/src/D3 Plotting Functions/drawLines.ts	
@@ -15,7 +15,7 @@ export default function drawLines(selection: svgBaseType, visualObj: Visual) {
         const upper: number = visualObj.viewModel.plotProperties.yAxis.upper;
         return d3.line<lineData>()
                   .x(d => visualObj.viewModel.plotProperties.xScale(d.x))
-                  .y(d => visualObj.viewModel.plotProperties.yScale(d.line_value))
+                  .y(d => visualObj.viewModel.plotProperties.yScale(d.line_value as number))
                   .defined(d => d.line_value !== null && between(d.line_value, lower, upper))(d[1])
       })
       .attr("fill", "none")
diff --git a/src/D3 Plotting Functions/drawTooltipLine.ts b/src/D3 Plotting Functions/drawTooltipLine.ts
index e19cc8f..e0d4dc5 100644
--- a/src/D3 Plotting Functions/drawTooltipLine.ts	
+++ b/src/D3 Plotting Functions/drawTooltipLine.ts	
@@ -32,7 +32,7 @@ export default function drawTooltipLine(selection: svgBaseType, visualObj: Visua
 
     const xValue: number = plotProperties.xScale.invert(event.pageX);
     const xRange: number[] = plotPoints.map(d => d.x).map(d => Math.abs(d - xValue));
-    const nearestDenominator: number = d3.leastIndex(xRange,(a,b) => a-b);
+    const nearestDenominator: number = d3.leastIndex(xRange,(a,b) => a-b) as number;
     const x_coord: number = plotProperties.xScale(plotPoints[nearestDenominator].x)
     const y_coord: number = plotProperties.yScale(plotPoints[nearestDenominator].value)
 
diff --git a/src/D3 Plotting Functions/drawYAxis.ts b/src/D3 Plotting Functions/drawYAxis.ts
index 56a8ce1..ffb14bf 100644
--- a/src/D3 Plotting Functions/drawYAxis.ts	
+++ b/src/D3 Plotting Functions/drawYAxis.ts	
@@ -18,10 +18,10 @@ export default function drawYAxis(selection: svgBaseType, visualObj: Visual, ref
     }
     if (visualObj.viewModel.inputData) {
       yAxis.tickFormat(
-        (d: number) => {
+        (d: d3.NumberValue) => {
           return visualObj.viewModel.inputData.percentLabels
-            ? (d * (multiplier === 100 ? 1 : (multiplier === 1 ? 100 : multiplier))).toFixed(sig_figs) + "%"
-            : d.toFixed(sig_figs);
+            ? (<number>d * (multiplier === 100 ? 1 : (multiplier === 1 ? 100 : multiplier))).toFixed(sig_figs) + "%"
+            : (<number>d).toFixed(sig_figs);
         }
       );
     }
diff --git a/src/D3 Plotting Functions/updateHighlighting.ts b/src/D3 Plotting Functions/updateHighlighting.ts
index 5a9bf47..19d4efc 100644
--- a/src/D3 Plotting Functions/updateHighlighting.ts	
+++ b/src/D3 Plotting Functions/updateHighlighting.ts	
@@ -1,8 +1,11 @@
 import powerbi from "powerbi-visuals-api";
+import * as d3 from "./D3 Modules"
 import { plotData } from "../Classes/viewModelClass";
 import ISelectionId = powerbi.visuals.ISelectionId;
 import { svgBaseType, Visual } from "../visual";
 
+type dotSelection = d3.Selection<SVGCircleElement, plotData, d3.BaseType, unknown>
+
 export default function updateHighlighting(selection: svgBaseType, visualObj: Visual) {
   const anyHighlights: boolean = visualObj.viewModel.inputData ? visualObj.viewModel.inputData.anyHighlights : false;
   const allSelectionIDs: ISelectionId[] = visualObj.selectionManager.getSelectionIds() as ISelectionId[];
@@ -16,7 +19,8 @@ export default function updateHighlighting(selection: svgBaseType, visualObj: Vi
   selection.selectAll(".dotsgroup").selectChildren().style("fill-opacity", defaultOpacity);
   selection.selectAll(".linesgroup").style("stroke-opacity", defaultOpacity);
   if (anyHighlights || (allSelectionIDs.length > 0)) {
-    selection.selectAll(".dotsgroup").selectChildren().style("fill-opacity", (dot: plotData) => {
+    const dotSelection: dotSelection = selection.selectAll(".dotsgroup").selectChildren();
+    dotSelection.style("fill-opacity", (dot: any) => {
       const currentPointSelected: boolean = allSelectionIDs.some((currentSelectionId: ISelectionId) => {
         return currentSelectionId.includes(dot.identity);
       });
diff --git a/src/Functions/BinaryFunctions.ts b/src/Functions/BinaryFunctions.ts
index 01a597b..3e0fa76 100644
--- a/src/Functions/BinaryFunctions.ts
+++ b/src/Functions/BinaryFunctions.ts
@@ -1,4 +1,4 @@
-type ReturnT<Input1T, Input2T, BaseT> = Input1T extends Array<any> ? BaseT[] : Input2T extends Array<any> ? BaseT[] : BaseT;
+type ReturnT<Input1T, Input2T, BaseT> = Input1T extends Array<any> ? NonNullable<BaseT>[] : Input2T extends Array<any> ? NonNullable<BaseT>[] : NonNullable<BaseT>;
 
 export default function broadcast_binary<ScalarInput1T, ScalarInput2T, ScalarReturnT>(fun: (x: ScalarInput1T, y: ScalarInput2T) => ScalarReturnT) {
   return function<T1 extends ScalarInput1T | ScalarInput1T[],
@@ -27,6 +27,6 @@ export const add = broadcast_binary((x: number, y: number): number => x + y);
 export const subtract = broadcast_binary((x: number, y: number): number => x - y);
 export const divide = broadcast_binary((x: number, y: number): number => x / y);
 export const multiply = broadcast_binary(
-  (x: number, y: number): number => {
+  (x: number, y: number): number | null => {
     return (x === null || y === null) ? null : (x * y);
 });
diff --git a/src/Functions/Constants.ts b/src/Functions/Constants.ts
index cd2653c..8bee7e2 100644
--- a/src/Functions/Constants.ts
+++ b/src/Functions/Constants.ts
@@ -2,28 +2,23 @@ import { sqrt, exp, lgamma, square } from "./UnaryFunctions";
 import broadcast_unary from "./UnaryFunctions";
 import broadcast_binary from "./BinaryFunctions";
 
-export const c4 = broadcast_unary(
-  (sampleSize: number): number => {
-    if ((sampleSize <= 1) || (sampleSize === null)) {
-      return null;
-    }
-    const Nminus1: number = sampleSize - 1;
+function c4(sampleSize: number): number {
+  const Nminus1: number = sampleSize - 1;
 
-    return sqrt(2.0 / Nminus1)
-            * exp(lgamma(sampleSize / 2.0) - lgamma(Nminus1 / 2.0));
-  }
-);
+  return sqrt(2.0 / Nminus1)
+          * exp(lgamma(sampleSize / 2.0) - lgamma(Nminus1 / 2.0));
+}
 
-export const c5 = broadcast_unary(
-  (sampleSize: number): number => {
-    return sqrt(1 - square(c4(sampleSize)));
-  }
-);
+function c5(sampleSize: number): number {
+  return sqrt(1 - square(c4(sampleSize) as number));
+}
 
 export const a3 = broadcast_unary(
-  (sampleSize: number): number => {
-    const filt_samp: number = sampleSize  <= 1 ? null : sampleSize;
-    return 3.0 / (c4(filt_samp) * sqrt(filt_samp));
+  (sampleSize: number): number | null => {
+    if ((sampleSize === null) || (sampleSize <= 1)) {
+      return null;
+    }
+    return 3.0 / (c4(sampleSize) as number * sqrt(sampleSize));
   }
 );
 
@@ -35,13 +30,19 @@ const b_helper = broadcast_binary(
 )
 
 export const b3 = broadcast_binary(
-  (sampleSize: number, use95: boolean): number => {
+  (sampleSize: number, use95: boolean): number | null => {
+    if ((sampleSize === null) || (sampleSize <= 1)) {
+      return null;
+    }
     return 1 - b_helper(sampleSize, use95);
   }
 );
 
 export const b4 = broadcast_binary(
-  (sampleSize: number, use95: boolean): number => {
+  (sampleSize: number, use95: boolean): number | null => {
+    if ((sampleSize === null) || (sampleSize <= 1)) {
+      return null;
+    }
     return 1 + b_helper(sampleSize, use95);
   }
 );
diff --git a/src/Functions/UnaryFunctions.ts b/src/Functions/UnaryFunctions.ts
index 34552d1..d6d2cd2 100644
--- a/src/Functions/UnaryFunctions.ts
+++ b/src/Functions/UnaryFunctions.ts
@@ -1,6 +1,6 @@
 import gammaln from "@stdlib/math-base-special-gammaln";
 
-type ReturnT<InputT, BaseT> = InputT extends Array<any> ? BaseT[] : BaseT;
+type ReturnT<InputT, BaseT> = InputT extends Array<any> ? NonNullable<BaseT>[] : NonNullable<BaseT>;
 
 export default function broadcast_unary<ScalarInputT, ScalarReturnT>(fun: (x: ScalarInputT) => ScalarReturnT) {
   return function<T extends ScalarInputT | ScalarInputT[]>(y: T): ReturnT<T, ScalarReturnT> {
diff --git a/src/Functions/buildTooltip.ts b/src/Functions/buildTooltip.ts
index 84136d9..fb23420 100644
--- a/src/Functions/buildTooltip.ts
+++ b/src/Functions/buildTooltip.ts
@@ -26,8 +26,8 @@ export default function buildTooltip(index: number, controlLimits: controlLimits
 
   const date: string = controlLimits.keys[index].label;
   const value: number = controlLimits.values[index];
-  const numerator: number = controlLimits.numerators ? controlLimits.numerators[index] : null;
-  const denominator: number = controlLimits.denominators ? controlLimits.denominators[index] : null;
+  const numerator: number | null = controlLimits.numerators ? controlLimits.numerators[index] : null;
+  const denominator: number | null = controlLimits.denominators ? controlLimits.denominators[index] : null;
   const target: number = controlLimits.targets[index];
   const limits = {
       ll99: controlLimits.ll99 ? controlLimits.ll99[index] : null,
@@ -71,7 +71,7 @@ export default function buildTooltip(index: number, controlLimits: controlLimits
   if (chart_type !== "run") {
     tooltip.push({
       displayName: "Upper 99% Limit",
-      value: (limits.ul99 * multiplier).toFixed(sig_figs) + suffix
+      value: (limits.ul99 !== null) ? (limits.ul99 * multiplier).toFixed(sig_figs) + suffix : ""
     })
   }
   tooltip.push({
@@ -81,7 +81,7 @@ export default function buildTooltip(index: number, controlLimits: controlLimits
   if (chart_type !== "run") {
     tooltip.push({
       displayName: "Lower 99% Limit",
-      value: (limits.ll99 * multiplier).toFixed(sig_figs) + suffix
+      value: (limits.ll99 !== null) ? (limits.ll99 * multiplier).toFixed(sig_figs) + suffix : ""
     })
   }
 
diff --git a/src/Functions/checkInvalidDataView.ts b/src/Functions/checkInvalidDataView.ts
index 6469d21..4f0bc82 100644
--- a/src/Functions/checkInvalidDataView.ts
+++ b/src/Functions/checkInvalidDataView.ts
@@ -12,21 +12,17 @@ export default function checkInvalidDataView(inputDV: powerbi.DataView[]): boole
     return flag1;
   }
 
-  const flag2: boolean =
-    !inputDV[0].categorical.categories[0].source
+  const inputView: powerbi.DataViewCategorical = inputDV[0].categorical as powerbi.DataViewCategorical;
+  const inputCategories: powerbi.DataViewCategoryColumn[] = inputView.categories as powerbi.DataViewCategoryColumn[];
+  const inputValues: powerbi.DataViewValueColumns = inputView.values as powerbi.DataViewValueColumns;
 
-  if (flag2) {
-    return flag2;
+  if (!inputCategories[0].source) {
+    return true;
   }
-  const flag3: boolean =
-    !inputDV[0].categorical.values[0].source.roles.numerators
 
-  if (flag3) {
-    return flag3;
+  if (!(inputValues[0].source.roles as Record<string, boolean>).numerators) {
+    return true;
   }
 
-  const flag4: boolean =
-    inputDV[0].categorical.values.some(d => d.values.length < 1)
-    || inputDV[0].categorical.categories.some(d => d.values.length < 1);
-  return flag4;
+  return inputValues.some(d => d.values.length < 1) || inputCategories.some(d => d.values.length < 1);
 }
diff --git a/src/Functions/checkValidInput.ts b/src/Functions/checkValidInput.ts
index 6499f65..3141333 100644
--- a/src/Functions/checkValidInput.ts
+++ b/src/Functions/checkValidInput.ts
@@ -1,4 +1,4 @@
-export default function checkValidInput(numerator: number, denominator: number, xbar_sd: number, data_type: string): boolean {
+export default function checkValidInput(numerator: number, denominator: number | null, xbar_sd: number | null, data_type: string): boolean {
   const denominatorConstraintRequired: string[] = ["p", "pprime", "u", "uprime"];
   const denominatorRequired: string[] = ["p", "pprime", "u", "uprime", "xbar", "s"];
   const denominatorConstraintForRunIChart: string[] = ["i", "run"];
@@ -7,7 +7,7 @@ export default function checkValidInput(numerator: number, denominator: number,
     ? denominator !== null && denominator !== undefined && denominator > 0
     : true;
   const proportionDenominatorValid: boolean = denominatorConstraintRequired.includes(data_type)
-    ? (numerator <= denominator)
+    ? (numerator <= (denominator as number))
     : true;
   const runIChartDenominatorValid: boolean
     = (denominatorConstraintForRunIChart.includes(data_type) && !(denominator === null))
diff --git a/src/Functions/dateToFormattedString.ts b/src/Functions/dateToFormattedString.ts
index b58d626..43ce182 100644
--- a/src/Functions/dateToFormattedString.ts
+++ b/src/Functions/dateToFormattedString.ts
@@ -49,7 +49,7 @@ const dateToFormattedString = broadcast_binary(
     const formatString: string = `{ ${localeDateMap[inpLocale]}, "options": { "day" : "2-digit", ${monthDateMap[inpMonth]}, ${yearDateMap[inpYear]} }, ${delimDateMap[inpDelim]} }`;
     const date_format: dateFormat = JSON.parse(formatString);
     const formattedString: string = input_date.toLocaleDateString(date_format.locale, date_format.options)
-                                              .replace(/(\/|(\s|,\s))/gi, date_format.delimiter);
+                                              .replace(/(\/|(\s|,\s))/gi, date_format.delimiter as string);
     if (inpDay !== "DD") {
       const weekday: string = input_date.toLocaleDateString(date_format.locale, {weekday : weekdayDateMap[inpDay]})
       return weekday + " " + formattedString;
diff --git a/src/Functions/diff.ts b/src/Functions/diff.ts
index 73e6a07..cb5b0b1 100644
--- a/src/Functions/diff.ts
+++ b/src/Functions/diff.ts
@@ -1,7 +1,3 @@
 export default function diff(x: number[]): number[] {
-  const consec_diff: number[] = new Array<number>(x.length - 1);
-  for (let i = 1; i < x.length;  i++) {
-    consec_diff[(i-1)] = (x[i] - x[(i-1)]);
-  }
-  return [<number>null].concat(consec_diff);
+  return x.map((d, idx, arr) => idx > 0 ? d - arr[idx - 1] : null) as number[]
 }
diff --git a/src/Functions/extractConditionalFormatting.ts b/src/Functions/extractConditionalFormatting.ts
index 3fbf3d7..daa37e8 100644
--- a/src/Functions/extractConditionalFormatting.ts
+++ b/src/Functions/extractConditionalFormatting.ts
@@ -8,12 +8,6 @@ import defaultSettings, { defaultSettingsType, defaultSettingsKey } from "../def
 type SettingsTypes = defaultSettingsType[defaultSettingsKey];
 
 export default function extractConditionalFormatting(categoricalView: DataViewCategorical, name: string, inputSettings: settingsClass): SettingsTypes[] {
-  if (categoricalView === null) {
-    return [null];
-  }
-  if ((categoricalView.categories === null) || (categoricalView.categories === undefined)) {
-    return [null];
-  }
   const inputCategories: DataViewCategoryColumn = (categoricalView.categories as DataViewCategoryColumn[])[0];
   const settingNames = Object.getOwnPropertyNames(inputSettings[name]);
 
diff --git a/src/Functions/extractDataColumn.ts b/src/Functions/extractDataColumn.ts
index c9193f4..a22c306 100644
--- a/src/Functions/extractDataColumn.ts
+++ b/src/Functions/extractDataColumn.ts
@@ -29,22 +29,22 @@ export default function extractDataColumn<T extends TargetT>(inputView: DataView
     } else {
       columnRaw = columnRawTmp[0];
     }
-    if (columnRaw.source.type.dateTime) {
+    if (columnRaw.source.type?.dateTime) {
       return dateToFormattedString(<Date[]>columnRaw.values, inputSettings.dates) as Extract<T, string[]>;
     } else {
       return <string[]>columnRaw.values as Extract<T, string[]>;
     }
   } else if (name === "tooltips") {
     let rtn = new Array<VisualTooltipDataItem[]>();
-    const tooltipColumns = inputView.values.filter(viewColumn => viewColumn.source.roles.tooltips);
+    const tooltipColumns = inputView.values!.filter(viewColumn => viewColumn.source.roles?.tooltips);
     if (tooltipColumns.length > 0) {
       rtn = tooltipColumns[0].values.map((_, idx) => {
         return tooltipColumns.map(viewColumn => {
           return <VisualTooltipDataItem>{
             displayName: viewColumn.source.displayName,
-            value: viewColumn.source.type.numeric
+            value: viewColumn.source.type?.numeric
                     ? (<number>(viewColumn.values[idx])).toString()
-                    : viewColumn.source.type.dateTime
+                    : viewColumn.source.type?.dateTime
                       ? dateToFormattedString(<Date>(viewColumn.values[idx]), inputSettings.dates)
                       : <string>(viewColumn.values[idx])
           }
diff --git a/src/Functions/isNotNullOrUndefined.ts b/src/Functions/isNotNullOrUndefined.ts
new file mode 100644
index 0000000..9e18bee
--- /dev/null
+++ b/src/Functions/isNotNullOrUndefined.ts
@@ -0,0 +1,3 @@
+export default function isNotNullOrUndefined<T>(x: T | null | undefined): x is T {
+  return (x !== null) && (x !== undefined);
+}
diff --git a/src/Limit Calculations/mr.ts b/src/Limit Calculations/mr.ts
index 1759bd9..8e990c9 100644
--- a/src/Limit Calculations/mr.ts	
+++ b/src/Limit Calculations/mr.ts	
@@ -20,8 +20,8 @@ export default function mrLimits(inputData: dataClass, inputSettings: settingsCl
     inputSettings: inputSettings,
     keys: inputData.keys,
     values: consec_diff,
-    numerators: useRatio ? inputData.numerators : null,
-    denominators: useRatio ? inputData.denominators : null,
+    numerators: useRatio ? inputData.numerators : undefined,
+    denominators: useRatio ? inputData.denominators : undefined,
     targets: rep(cl, inputData.keys.length),
     ll99: rep(0, inputData.keys.length),
     ll95: rep(0, inputData.keys.length),
diff --git a/src/Limit Calculations/run.ts b/src/Limit Calculations/run.ts
index 2479152..1731570 100644
--- a/src/Limit Calculations/run.ts	
+++ b/src/Limit Calculations/run.ts	
@@ -16,12 +16,12 @@ export default function runLimits(inputData: dataClass, inputSettings: settingsC
     inputSettings: inputSettings,
     keys: inputData.keys,
     values: ratio.map(d => isNaN(d) ? 0 : d),
-    numerators: useRatio ? inputData.numerators : <number[]>null,
-    denominators: useRatio ? inputData.denominators : <number[]>null,
+    numerators: useRatio ? inputData.numerators : undefined,
+    denominators: useRatio ? inputData.denominators : undefined,
     targets: rep(cl, inputData.keys.length),
-    ll99: <number[]>null,
-    ll95: <number[]>null,
-    ul95: <number[]>null,
-    ul99: <number[]>null
+    ll99: new Array<number>(),
+    ll95: new Array<number>(),
+    ul95: new Array<number>(),
+    ul99: new Array<number>()
   });
 }
diff --git a/src/Limit Calculations/t.ts b/src/Limit Calculations/t.ts
index 4037f45..4b1af49 100644
--- a/src/Limit Calculations/t.ts	
+++ b/src/Limit Calculations/t.ts	
@@ -9,7 +9,7 @@ export default function tLimits(inputData: dataClass, inputSettings: settingsCla
   const val: number[] = pow(inputData.numerators, 1 / 3.6);
   const inputDataCopy: dataClass = JSON.parse(JSON.stringify(inputData));
   inputDataCopy.numerators = val;
-  inputDataCopy.denominators = null;
+  inputDataCopy.denominators = new Array<number>();
   const limits: controlLimitsClass = iLimits(inputDataCopy, inputSettings);
   limits.targets = pow(limits.targets, 3.6);
   limits.values = pow(limits.values, 3.6);
diff --git a/src/defaultSettings.ts b/src/defaultSettings.ts
index b2823eb..1892747 100644
--- a/src/defaultSettings.ts
+++ b/src/defaultSettings.ts
@@ -12,9 +12,9 @@ const defaultSettings = {
     sig_figs: 2,
     perc_labels: "Automatic",
     split_on_click: false,
-    ll_truncate: <number>(null),
-    ul_truncate: <number>(null),
-    alt_target: <number>(null)
+    ll_truncate: <number><unknown>(null),
+    ul_truncate: <number><unknown>(null),
+    alt_target: <number><unknown>(null)
   },
   outliers: {
     process_flag_type: "both",
@@ -81,13 +81,13 @@ const defaultSettings = {
     xlimit_tick_size: 10,
     xlimit_tick_colour: "#000000",
     xlimit_tick_rotation: -35,
-    xlimit_tick_count: <number>(null),
-    xlimit_label:<string>(null),
+    xlimit_tick_count: <number><unknown>(null),
+    xlimit_label:"",
     xlimit_label_font: "'Arial', sans-serif",
     xlimit_label_size: 10,
     xlimit_label_colour: "#000000",
-    xlimit_l: <number>(null),
-    xlimit_u: <number>(null)
+    xlimit_l: <number><unknown>(null),
+    xlimit_u: <number><unknown>(null)
   },
   y_axis: {
     ylimit_colour: "#000000",
@@ -96,15 +96,15 @@ const defaultSettings = {
     ylimit_tick_size: 10,
     ylimit_tick_colour: "#000000",
     ylimit_tick_rotation: -35,
-    ylimit_tick_count: <number>(null),
-    ylimit_label:<string>(null),
+    ylimit_tick_count: <number><unknown>(null),
+    ylimit_label:"",
     ylimit_label_font: "'Arial', sans-serif",
     ylimit_label_size: 10,
     ylimit_label_colour: "#000000",
-    ylimit_l: <number>(null),
-    ylimit_u: <number>(null),
+    ylimit_l: <number><unknown>(null),
+    ylimit_u: <number><unknown>(null),
     limit_multiplier: 1.5,
-    ylimit_sig_figs: <number>(null)
+    ylimit_sig_figs: <number><unknown>(null)
   },
   dates: {
     date_format_day: "DD",
diff --git a/tsconfig.json b/tsconfig.json
index b68a445..e5f062b 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -9,6 +9,7 @@
         "noImplicitThis": true,
         "noUnusedLocals": true,
         "noUnusedParameters": true,
+        "noImplicitOverride": true,
         "strictBindCallApply": true,
         "emitDecoratorMetadata": true,
         "experimentalDecorators": true,