diff --git a/src/Menees.Diffs.Windows.Forms/Caret.cs b/src/Menees.Diffs.Windows.Forms/Caret.cs
index 5cf1da6..aa125bb 100644
--- a/src/Menees.Diffs.Windows.Forms/Caret.cs
+++ b/src/Menees.Diffs.Windows.Forms/Caret.cs
@@ -129,7 +129,7 @@ public void Dispose()
 
 		#region Private Methods
 
-		private void ControlGotFocus(object sender, EventArgs e)
+		private void ControlGotFocus(object? sender, EventArgs e)
 		{
 			// Sometimes in the debugger, we'll get focus without ever having been sent
 			// the LostFocus event.  So I'll fire it now just to make things balance out.
@@ -146,7 +146,7 @@ private void ControlGotFocus(object sender, EventArgs e)
 			}
 		}
 
-		private void ControlLostFocus(object sender, EventArgs e)
+		private void ControlLostFocus(object? sender, EventArgs e)
 		{
 			if (this.createdCaret)
 			{
diff --git a/src/Menees.Diffs.Windows.Forms/DiffControl.cs b/src/Menees.Diffs.Windows.Forms/DiffControl.cs
index d38b51e..ff52dab 100644
--- a/src/Menees.Diffs.Windows.Forms/DiffControl.cs
+++ b/src/Menees.Diffs.Windows.Forms/DiffControl.cs
@@ -49,11 +49,11 @@ public DiffControl()
 
 		#region Public Events
 
-		public event EventHandler LineDiffSizeChanged;
+		public event EventHandler? LineDiffSizeChanged;
 
-		public event EventHandler RecompareNeeded;
+		public event EventHandler? RecompareNeeded;
 
-		public event EventHandler<DifferenceEventArgs> ShowTextDifferences;
+		public event EventHandler<DifferenceEventArgs>? ShowTextDifferences;
 
 		#endregion
 
@@ -163,11 +163,6 @@ public bool ShowToolBar
 		}
 
 		[DefaultValue(false)]
-		[SuppressMessage(
-			"Microsoft.Naming",
-			"CA1702:CompoundWordsShouldBeCasedCorrectly",
-			MessageId = "InLine",
-			Justification = "'inline' is not an appropriate term here.")]
 		public bool ShowWhiteSpaceInLineDiff
 		{
 			get
@@ -258,7 +253,7 @@ public bool CompareSelectedText()
 				string textB = this.ViewB.SelectedText;
 
 				DifferenceEventArgs diffArgs = new(textA, textB);
-				this.ShowTextDifferences(this, diffArgs);
+				this.ShowTextDifferences?.Invoke(this, diffArgs);
 				result = true;
 			}
 
@@ -307,7 +302,7 @@ public bool Recompare()
 
 			if (this.CanRecompare)
 			{
-				this.RecompareNeeded(this, EventArgs.Empty);
+				this.RecompareNeeded?.Invoke(this, EventArgs.Empty);
 				result = true;
 			}
 
@@ -402,7 +397,7 @@ public void ViewFile()
 
 		#region Internal Methods
 
-		internal static void PaintColorLegendItem(ToolStripItem item, PaintEventArgs e)
+		internal static void PaintColorLegendItem(ToolStripItem? item, PaintEventArgs e)
 		{
 			if (item != null)
 			{
@@ -434,57 +429,57 @@ internal static void PaintColorLegendItem(ToolStripItem item, PaintEventArgs e)
 
 		#region Private Methods
 
-		private void Copy_Click(object sender, EventArgs e)
+		private void Copy_Click(object? sender, EventArgs e)
 		{
 			this.Copy();
 		}
 
-		private void Find_Click(object sender, EventArgs e)
+		private void Find_Click(object? sender, EventArgs e)
 		{
 			this.Find();
 		}
 
-		private void FindNext_Click(object sender, EventArgs e)
+		private void FindNext_Click(object? sender, EventArgs e)
 		{
 			this.FindNext();
 		}
 
-		private void FindPrevious_Click(object sender, EventArgs e)
+		private void FindPrevious_Click(object? sender, EventArgs e)
 		{
 			this.FindPrevious();
 		}
 
-		private void FirstDiff_Click(object sender, EventArgs e)
+		private void FirstDiff_Click(object? sender, EventArgs e)
 		{
 			this.GoToFirstDiff();
 		}
 
-		private void GotoLine_Click(object sender, EventArgs e)
+		private void GotoLine_Click(object? sender, EventArgs e)
 		{
 			this.GoToLine();
 		}
 
-		private void LastDiff_Click(object sender, EventArgs e)
+		private void LastDiff_Click(object? sender, EventArgs e)
 		{
 			this.GoToLastDiff();
 		}
 
-		private void NextDiff_Click(object sender, EventArgs e)
+		private void NextDiff_Click(object? sender, EventArgs e)
 		{
 			this.GoToNextDiff();
 		}
 
-		private void PrevDiff_Click(object sender, EventArgs e)
+		private void PrevDiff_Click(object? sender, EventArgs e)
 		{
 			this.GoToPreviousDiff();
 		}
 
-		private void Recompare_Click(object sender, EventArgs e)
+		private void Recompare_Click(object? sender, EventArgs e)
 		{
 			this.Recompare();
 		}
 
-		private void ViewFile_Click(object sender, EventArgs e)
+		private void ViewFile_Click(object? sender, EventArgs e)
 		{
 			this.ViewFile();
 		}
@@ -495,17 +490,17 @@ private void ColorLegend_Paint(object sender, PaintEventArgs e)
 			PaintColorLegendItem(sender as ToolStripItem, e);
 		}
 
-		private void DiffControl_SizeChanged(object sender, EventArgs e)
+		private void DiffControl_SizeChanged(object? sender, EventArgs e)
 		{
 			this.pnlLeft.Width = (this.Width - this.pnlLeft.Left - this.MiddleSplitter.Width) / 2;
 		}
 
-		private void DiffOptionsChanged(object sender, EventArgs e)
+		private void DiffOptionsChanged(object? sender, EventArgs e)
 		{
 			this.UpdateColors();
 		}
 
-		private void TextDiff_Click(object sender, EventArgs e)
+		private void TextDiff_Click(object? sender, EventArgs e)
 		{
 			this.CompareSelectedText();
 		}
@@ -555,11 +550,11 @@ private void UpdateLineDiff()
 			{
 				this.currentDiffLine = line;
 
-				DiffViewLine lineOne = null;
-				DiffViewLine lineTwo = null;
+				DiffViewLine? lineOne = null;
+				DiffViewLine? lineTwo = null;
 				if (line < this.ViewA.LineCount)
 				{
-					lineOne = this.ViewA.Lines[line];
+					lineOne = this.ViewA.Lines?[line];
 				}
 
 				// Normally, ViewA.LineCount == ViewB.LineCount, but during
@@ -567,7 +562,7 @@ private void UpdateLineDiff()
 				// rebuilds its lines.
 				if (line < this.ViewB.LineCount)
 				{
-					lineTwo = this.ViewB.Lines[line];
+					lineTwo = this.ViewB.Lines?[line];
 				}
 
 				if (lineOne != null && lineTwo != null)
@@ -577,7 +572,7 @@ private void UpdateLineDiff()
 			}
 		}
 
-		private void View_PositionChanged(object sender, EventArgs e)
+		private void View_PositionChanged(object? sender, EventArgs e)
 		{
 			DiffView view = this.ActiveView;
 			DiffViewPosition pos = view.Position;
@@ -590,27 +585,27 @@ private void View_PositionChanged(object sender, EventArgs e)
 			}
 		}
 
-		private void ViewA_HScrollPosChanged(object sender, EventArgs e)
+		private void ViewA_HScrollPosChanged(object? sender, EventArgs e)
 		{
 			this.ViewB.HScrollPos = this.ViewA.HScrollPos;
 		}
 
-		private void ViewA_VScrollPosChanged(object sender, EventArgs e)
+		private void ViewA_VScrollPosChanged(object? sender, EventArgs e)
 		{
 			this.ViewB.VScrollPos = this.ViewA.VScrollPos;
 		}
 
-		private void ViewB_HScrollPosChanged(object sender, EventArgs e)
+		private void ViewB_HScrollPosChanged(object? sender, EventArgs e)
 		{
 			this.ViewA.HScrollPos = this.ViewB.HScrollPos;
 		}
 
-		private void ViewB_VScrollPosChanged(object sender, EventArgs e)
+		private void ViewB_VScrollPosChanged(object? sender, EventArgs e)
 		{
 			this.ViewA.VScrollPos = this.ViewB.VScrollPos;
 		}
 
-		private void ViewLineDiff_SizeChanged(object sender, EventArgs e)
+		private void ViewLineDiff_SizeChanged(object? sender, EventArgs e)
 		{
 			this.LineDiffSizeChanged?.Invoke(this, e);
 		}
diff --git a/src/Menees.Diffs.Windows.Forms/DiffOptions.cs b/src/Menees.Diffs.Windows.Forms/DiffOptions.cs
index c391c9f..a28f413 100644
--- a/src/Menees.Diffs.Windows.Forms/DiffOptions.cs
+++ b/src/Menees.Diffs.Windows.Forms/DiffOptions.cs
@@ -37,7 +37,7 @@ public static class DiffOptions
 
 		#region Public Events
 
-		public static event EventHandler OptionsChanged;
+		public static event EventHandler? OptionsChanged;
 
 		#endregion
 
@@ -211,9 +211,9 @@ public static void Save(ISettingsNode node)
 			node.SetValue(nameof(HatchDeadSpace), HatchDeadSpace);
 		}
 
-		public static Brush TryCreateDeadSpaceBrush(Color backColor)
+		public static Brush? TryCreateDeadSpaceBrush(Color backColor)
 		{
-			Brush result = null;
+			Brush? result = null;
 			if (HatchDeadSpace)
 			{
 				result = new HatchBrush(HatchStyle.Percent25, SystemColors.ControlDark, backColor);
diff --git a/src/Menees.Diffs.Windows.Forms/DiffOverview.cs b/src/Menees.Diffs.Windows.Forms/DiffOverview.cs
index 034ed23..0cb61a8 100644
--- a/src/Menees.Diffs.Windows.Forms/DiffOverview.cs
+++ b/src/Menees.Diffs.Windows.Forms/DiffOverview.cs
@@ -21,8 +21,8 @@ internal sealed class DiffOverview : Control
 		private readonly BorderStyle borderStyle = BorderStyle.Fixed3D;
 		private bool dragging;
 		private bool useTranslucentView = true;
-		private Bitmap image;
-		private DiffView view;
+		private Bitmap? image;
+		private DiffView? view;
 		private Rectangle viewRect;
 
 		#endregion
@@ -52,17 +52,13 @@ public DiffOverview()
 		/// <summary>
 		/// Fired when the user clicks and/or drags to move the view.
 		/// </summary>
-		public event EventHandler<DiffLineClickEventArgs> LineClick;
+		public event EventHandler<DiffLineClickEventArgs>? LineClick;
 
 		#endregion
 
 		#region Public Properties
 
-		[SuppressMessage(
-			"Microsoft.Performance",
-			"CA1811:AvoidUncalledPrivateCode",
-			Justification = "The get_DiffView accessor is only called by the Windows Forms designer via reflection.")]
-		public DiffView DiffView
+		public DiffView? DiffView
 		{
 			get
 			{
@@ -212,7 +208,7 @@ protected override void OnPaint(PaintEventArgs e)
 				// Repaint the view window if any of it is invalid
 				if (r.IntersectsWith(this.viewRect))
 				{
-					Pen disposablePen = null;
+					Pen? disposablePen = null;
 					try
 					{
 						Pen pen = SystemPens.Highlight;
@@ -289,7 +285,7 @@ private void CalculateViewRect()
 			}
 		}
 
-		private void DiffOptionsChanged(object sender, EventArgs e)
+		private void DiffOptionsChanged(object? sender, EventArgs e)
 		{
 			// The diff colors changed, so we need to rerender the
 			// image.  The current view rect should still be valid.
@@ -297,13 +293,13 @@ private void DiffOptionsChanged(object sender, EventArgs e)
 			this.Invalidate();
 		}
 
-		private void DiffView_LinesChanged(object sender, EventArgs e)
+		private void DiffView_LinesChanged(object? sender, EventArgs e)
 		{
 			// If the Lines changed, we need to update everything.
 			this.UpdateAll();
 		}
 
-		private void DiffView_SizeChanged(object sender, EventArgs e)
+		private void DiffView_SizeChanged(object? sender, EventArgs e)
 		{
 			// If the DiffView size changed, then our view window
 			// may be longer or shorter, but the rendered image is
@@ -313,7 +309,7 @@ private void DiffView_SizeChanged(object sender, EventArgs e)
 			this.Invalidate();
 		}
 
-		private void DiffView_VScrollPosChanged(object sender, EventArgs e)
+		private void DiffView_VScrollPosChanged(object? sender, EventArgs e)
 		{
 			// The DiffView's FirstVisibleLine has changed, so we
 			// just need to invalidate our view.
@@ -425,7 +421,7 @@ private void RenderImage()
 
 									// Draw delete on the left and dead space on the right.
 									g.FillRectangle(backBrush, GutterWidth, y, fullFillWidth / 2, lineHeight);
-									using (Brush deadBrush = DiffOptions.TryCreateDeadSpaceBrush(backBrush.Color))
+									using (Brush? deadBrush = DiffOptions.TryCreateDeadSpaceBrush(backBrush.Color))
 									{
 										g.FillRectangle(deadBrush ?? backBrush, GutterWidth + (fullFillWidth / 2), y, fullFillWidth / 2, lineHeight);
 									}
@@ -435,7 +431,7 @@ private void RenderImage()
 								case EditType.Insert:
 
 									// Draw dead space on the left and insert on the right.
-									using (Brush deadBrush = DiffOptions.TryCreateDeadSpaceBrush(backBrush.Color))
+									using (Brush? deadBrush = DiffOptions.TryCreateDeadSpaceBrush(backBrush.Color))
 									{
 										g.FillRectangle(deadBrush ?? backBrush, GutterWidth, y, fullFillWidth / 2, lineHeight);
 									}
diff --git a/src/Menees.Diffs.Windows.Forms/DiffView.Privates.cs b/src/Menees.Diffs.Windows.Forms/DiffView.Privates.cs
index a940ce7..2f02120 100644
--- a/src/Menees.Diffs.Windows.Forms/DiffView.Privates.cs
+++ b/src/Menees.Diffs.Windows.Forms/DiffView.Privates.cs
@@ -33,14 +33,14 @@ internal sealed partial class DiffView : Control
 		private readonly Timer autoScrollTimer;
 		private bool capturedMouse;
 		private bool showWhitespace;
-		private Caret caret;
+		private Caret? caret;
 		private int charWidth = 1;
 		private int gutterWidth = 1;
 		private int horizontalAutoScrollAmount;
 		private int lineHeight = 1;
 		private int verticalAutoScrollAmount;
 		private int wheelDelta;
-		private DiffViewLines lines;
+		private DiffViewLines? lines;
 		private DiffViewPosition position;
 		private DiffViewPosition selectionStart = DiffViewPosition.Empty;
 		private string gutterFormat = "{0}";
@@ -103,7 +103,7 @@ private static int MeasureString(Graphics g, string displayText, int length, Fon
 			return result.Width;
 		}
 
-		private void AutoScrollTimer_Tick(object sender, EventArgs e)
+		private void AutoScrollTimer_Tick(object? sender, EventArgs e)
 		{
 			this.VScrollPos += this.verticalAutoScrollAmount;
 			this.HScrollPos += this.horizontalAutoScrollAmount;
@@ -124,7 +124,7 @@ private void ClearSelection()
 			}
 		}
 
-		private void DiffOptionsChanged(object sender, EventArgs e)
+		private void DiffOptionsChanged(object? sender, EventArgs e)
 		{
 			// The colors and/or tab width changed.
 			this.UpdateTextMetrics(true);
@@ -140,7 +140,7 @@ private void DrawBackground(Graphics g, SolidBrush brush, int y, bool deadSpace)
 		{
 			if (deadSpace)
 			{
-				using (Brush deadBrush = DiffOptions.TryCreateDeadSpaceBrush(brush.Color))
+				using (Brush? deadBrush = DiffOptions.TryCreateDeadSpaceBrush(brush.Color))
 				{
 					// If hatching is turned off, then we have to fallback to the solid brush.
 					g.FillRectangle(deadBrush ?? brush, this.gutterWidth, y, this.ClientSize.Width, this.lineHeight);
@@ -271,7 +271,7 @@ private void DrawLine(
 				// extra work until the user requests to see the changed line.  It's still
 				// the same amount of work if they view every line, but it makes the
 				// user interface more responsive to split it up like this.
-				EditScript changeEditScript = line.GetChangeEditScript(this.ChangeDiffOptions);
+				EditScript? changeEditScript = line.GetChangeEditScript(this.ChangeDiffOptions);
 				if (changeEditScript != null)
 				{
 					this.DrawChangedLineBackground(g, displayLine, lineText, changeEditScript, line.FromA, x, y);
@@ -433,7 +433,7 @@ private void FireSelectionChanged()
 		private DisplayLine GetDisplayLine(int line)
 		{
 			DisplayLine result;
-			if (line >= 0 && line < this.LineCount)
+			if (line >= 0 && line < this.LineCount && this.lines != null)
 			{
 				result = this.GetDisplayLine(this.lines[line]);
 			}
@@ -499,7 +499,7 @@ private void GetForwardOrderSelection(out DiffViewPosition startSel, out DiffVie
 			}
 		}
 
-		private bool GetSingleLineSelectedText(out string text)
+		private bool GetSingleLineSelectedText(out string? text)
 		{
 			text = null;
 			bool result = false;
@@ -518,7 +518,7 @@ private bool GetSingleLineSelectedText(out string text)
 			return result;
 		}
 
-		private int GetXForColumn(Graphics g, DisplayLine displayLine, string displayText, int column)
+		private int GetXForColumn(Graphics g, DisplayLine displayLine, string? displayText, int column)
 		{
 			if (displayText == null)
 			{
@@ -884,7 +884,7 @@ private void UpdateTextMetrics(bool fontOrTabsChanged)
 			// pixel so we can have a separator line, and then
 			// a small separator window-colored area.
 			int maxLineNumChars = 1;
-			if (this.LineCount > 0)
+			if (this.LineCount > 0 && this.lines != null)
 			{
 				// Get the largest number.  Add 1 to it because we will
 				// when we display it.  This is important when the number
@@ -909,7 +909,7 @@ private void UpdateTextMetrics(bool fontOrTabsChanged)
 			StringBuilder sb = new(BufferSize);
 			sb.Append("{0:");
 			sb.Append('0', maxLineNumChars);
-			sb.Append("}");
+			sb.Append('}');
 			this.gutterFormat = sb.ToString();
 
 			// Update the caret position (Gutter width or Font changes affect it)
diff --git a/src/Menees.Diffs.Windows.Forms/DiffView.cs b/src/Menees.Diffs.Windows.Forms/DiffView.cs
index de62b73..f0d6d47 100644
--- a/src/Menees.Diffs.Windows.Forms/DiffView.cs
+++ b/src/Menees.Diffs.Windows.Forms/DiffView.cs
@@ -24,10 +24,6 @@ internal sealed partial class DiffView : Control
 	{
 		#region Constructors
 
-		[SuppressMessage(
-			"Microsoft.Mobility",
-			"CA1601:DoNotUseTimersThatPreventPowerStateChanges",
-			Justification = "This timer is only used to auto-scroll while the mouse is captured and dragging.")]
 		public DiffView()
 		{
 			// Set some important control styles
@@ -44,9 +40,11 @@ public DiffView()
 
 			this.UpdateTextMetrics(true);
 
-			this.autoScrollTimer = new Timer();
-			this.autoScrollTimer.Enabled = false;
-			this.autoScrollTimer.Interval = 100;
+			this.autoScrollTimer = new Timer
+			{
+				Enabled = false,
+				Interval = 100,
+			};
 			this.autoScrollTimer.Tick += this.AutoScrollTimer_Tick;
 
 			DiffOptions.OptionsChanged += this.DiffOptionsChanged;
@@ -58,15 +56,15 @@ public DiffView()
 
 		#region Public Events
 
-		public event EventHandler HScrollPosChanged;
+		public event EventHandler? HScrollPosChanged;
 
-		public event EventHandler LinesChanged;
+		public event EventHandler? LinesChanged;
 
-		public event EventHandler PositionChanged;
+		public event EventHandler? PositionChanged;
 
-		public event EventHandler SelectionChanged;
+		public event EventHandler? SelectionChanged;
 
-		public event EventHandler VScrollPosChanged;
+		public event EventHandler? VScrollPosChanged;
 
 		#endregion
 
@@ -143,10 +141,6 @@ public bool CanGoToPreviousDiff
 		}
 
 		[Browsable(false)]
-		[SuppressMessage(
-			"Microsoft.Performance",
-			"CA1811:AvoidUncalledPrivateCode",
-			Justification = "The get_CenterVisibleLine accessor is only called by the Windows Forms designer via reflection.")]
 		public int CenterVisibleLine
 		{
 			get
@@ -206,7 +200,7 @@ public int HScrollPos
 		/// Stores each line's text, color, and original number.
 		/// </summary>
 		[Browsable(false)]
-		public DiffViewLines Lines => this.lines;
+		public DiffViewLines? Lines => this.lines;
 
 		[Browsable(false)]
 		public DiffViewPosition Position
@@ -336,7 +330,7 @@ public bool Find(FindData data)
 		{
 			// If text is selected on a single line, then use that for the new Find text.
 			string originalFindText = data.Text;
-			if (this.GetSingleLineSelectedText(out string selectedText))
+			if (this.GetSingleLineSelectedText(out string? selectedText) && selectedText != null)
 			{
 				data.Text = selectedText;
 			}
@@ -617,7 +611,7 @@ public bool GoToFirstDiff()
 		{
 			bool result = false;
 
-			if (this.CanGoToFirstDiff)
+			if (this.CanGoToFirstDiff && this.lines != null)
 			{
 				this.GoToPosition(this.lines.DiffStartLines[0], this.position.Column);
 				result = true;
@@ -630,7 +624,7 @@ public bool GoToLastDiff()
 		{
 			bool result = false;
 
-			if (this.CanGoToLastDiff)
+			if (this.CanGoToLastDiff && this.lines != null)
 			{
 				int[] starts = this.lines.DiffStartLines;
 				this.GoToPosition(starts[starts.Length - 1], this.position.Column);
@@ -643,14 +637,17 @@ public bool GoToLastDiff()
 		public bool GoToLine()
 		{
 			int maxLineNumber = 0;
-			for (int i = this.lines.Count - 1; i >= 0; i--)
+			if (this.lines != null)
 			{
-				DiffViewLine line = this.lines[i];
-				if (line.Number.HasValue)
+				for (int i = this.lines.Count - 1; i >= 0; i--)
 				{
-					// Add 1 because display numbers are 1-based.
-					maxLineNumber = line.Number.Value + 1;
-					break;
+					DiffViewLine line = this.lines[i];
+					if (line.Number.HasValue)
+					{
+						// Add 1 because display numbers are 1-based.
+						maxLineNumber = line.Number.Value + 1;
+						break;
+					}
 				}
 			}
 
@@ -695,7 +692,7 @@ public bool GoToNextDiff()
 		{
 			bool result = false;
 
-			if (this.CanGoToNextDiff)
+			if (this.CanGoToNextDiff && this.lines != null)
 			{
 				int[] starts = this.lines.DiffStartLines;
 				int numStarts = starts.Length;
@@ -717,7 +714,7 @@ public bool GoToPreviousDiff()
 		{
 			bool result = false;
 
-			if (this.CanGoToPreviousDiff)
+			if (this.CanGoToPreviousDiff && this.lines != null)
 			{
 				int[] ends = this.lines.DiffEndLines;
 				int numEnds = ends.Length;
@@ -795,14 +792,17 @@ public void SetCounterpartLines(DiffView counterpartView)
 				throw new ArgumentException("The counterpart view has a different number of view lines.", nameof(counterpartView));
 			}
 
-			for (int i = 0; i < numLines; i++)
+			if (this.lines != null && counterpartView.lines != null)
 			{
-				DiffViewLine line = this.lines[i];
-				DiffViewLine counterpart = counterpartView.lines[i];
+				for (int i = 0; i < numLines; i++)
+				{
+					DiffViewLine line = this.lines[i];
+					DiffViewLine counterpart = counterpartView.lines[i];
 
-				// Make the counterpart lines refer to each other.
-				line.Counterpart = counterpart;
-				counterpart.Counterpart = line;
+					// Make the counterpart lines refer to each other.
+					line.Counterpart = counterpart;
+					counterpart.Counterpart = line;
+				}
 			}
 		}
 
@@ -1144,23 +1144,26 @@ protected override void OnPaint(PaintEventArgs e)
 				this.GetForwardOrderSelection(out DiffViewPosition startSel, out DiffViewPosition endSel);
 
 				// Paint each line
-				for (int i = firstLine; i <= lastLine; i++)
+				if (this.lines != null)
 				{
-					// If we get inside this loop there must be at least one line.
-					Debug.Assert(this.LineCount > 0, "There must be at least one line.");
+					for (int i = firstLine; i <= lastLine; i++)
+					{
+						// If we get inside this loop there must be at least one line.
+						Debug.Assert(this.LineCount > 0, "There must be at least one line.");
 
-					int x = (this.charWidth * (-posX)) + this.gutterWidth;
-					int y = this.lineHeight * (i - posY);
+						int x = (this.charWidth * (-posX)) + this.gutterWidth;
+						int y = this.lineHeight * (i - posY);
 
-					DiffViewLine line = this.lines[i];
-					if (paintLine)
-					{
-						this.DrawLine(g, fontBrush, backBrush, hasFocus, i, line, x, y, hasSelection, startSel, endSel);
-					}
+						DiffViewLine line = this.lines[i];
+						if (paintLine)
+						{
+							this.DrawLine(g, fontBrush, backBrush, hasFocus, i, line, x, y, hasSelection, startSel, endSel);
+						}
 
-					if (paintGutter)
-					{
-						this.DrawGutter(g, fontBrush, backBrush, hasFocus, i, line, y, gutterBrush, lineNumIndent);
+						if (paintGutter)
+						{
+							this.DrawGutter(g, fontBrush, backBrush, hasFocus, i, line, y, gutterBrush, lineNumIndent);
+						}
 					}
 				}
 
diff --git a/src/Menees.Diffs.Windows.Forms/DiffViewLine.cs b/src/Menees.Diffs.Windows.Forms/DiffViewLine.cs
index 249fbea..b7fa7f2 100644
--- a/src/Menees.Diffs.Windows.Forms/DiffViewLine.cs
+++ b/src/Menees.Diffs.Windows.Forms/DiffViewLine.cs
@@ -25,7 +25,7 @@ internal sealed class DiffViewLine
 		private readonly int? number;
 		private readonly string text;
 		private readonly EditType editType;
-		private EditScript changeEditScript;
+		private EditScript? changeEditScript;
 
 		#endregion
 
@@ -48,9 +48,8 @@ private DiffViewLine()
 
 		#region Public Properties
 
-		public DiffViewLine Counterpart { get; internal set; }
+		public DiffViewLine? Counterpart { get; internal set; }
 
-		[SuppressMessage("", "SA1101", Justification = "The EditType reference is to the type not to this.EditType.")]
 		public bool Edited => this.editType != EditType.None;
 
 		public EditType EditType => this.editType;
@@ -65,7 +64,7 @@ private DiffViewLine()
 
 		#region Public Methods
 
-		public EditScript GetChangeEditScript(ChangeDiffOptions options)
+		public EditScript? GetChangeEditScript(ChangeDiffOptions options)
 		{
 			if (this.changeEditScript == null && this.editType == EditType.Change && this.Counterpart != null)
 			{
@@ -188,7 +187,9 @@ public void Clear()
 				throw new NotSupportedException();
 			}
 
+#pragma warning disable CA2249 // Consider using 'string.Contains' instead of 'string.IndexOf'. net48 doesn't support Contains(string).
 			public bool Contains(char item) => this.text.IndexOf(item) >= 0;
+#pragma warning restore CA2249 // Consider using 'string.Contains' instead of 'string.IndexOf'
 
 			public void CopyTo(char[] array, int arrayIndex)
 			{
diff --git a/src/Menees.Diffs.Windows.Forms/DiffViewLines.cs b/src/Menees.Diffs.Windows.Forms/DiffViewLines.cs
index 66e8b5b..c44cb85 100644
--- a/src/Menees.Diffs.Windows.Forms/DiffViewLines.cs
+++ b/src/Menees.Diffs.Windows.Forms/DiffViewLines.cs
@@ -84,15 +84,14 @@ public DiffViewLines(DiffViewLine lineOne, DiffViewLine lineTwo)
 		{
 			this.AddLine(lineOne);
 			this.AddLine(lineTwo);
-
-			this.diffStartLines = CollectionUtility.EmptyArray<int>();
-			this.diffEndLines = CollectionUtility.EmptyArray<int>();
 		}
 
 		private DiffViewLines()
 			: base(new List<DiffViewLine>())
 		{
 			// Called by the other constructors.
+			this.diffStartLines = CollectionUtility.EmptyArray<int>();
+			this.diffEndLines = CollectionUtility.EmptyArray<int>();
 		}
 
 		#endregion
diff --git a/src/Menees.Diffs.Windows.Forms/DiffViewPosition.cs b/src/Menees.Diffs.Windows.Forms/DiffViewPosition.cs
index 27ab2a4..1fc9cef 100644
--- a/src/Menees.Diffs.Windows.Forms/DiffViewPosition.cs
+++ b/src/Menees.Diffs.Windows.Forms/DiffViewPosition.cs
@@ -89,7 +89,7 @@ public int CompareTo(DiffViewPosition position)
 			return result;
 		}
 
-		public override bool Equals(object value)
+		public override bool Equals(object? value)
 		{
 			bool result = false;
 
diff --git a/src/Menees.Diffs.Windows.Forms/DirectoryDiffControl.cs b/src/Menees.Diffs.Windows.Forms/DirectoryDiffControl.cs
index 46922cf..8bee5e6 100644
--- a/src/Menees.Diffs.Windows.Forms/DirectoryDiffControl.cs
+++ b/src/Menees.Diffs.Windows.Forms/DirectoryDiffControl.cs
@@ -43,9 +43,9 @@ public DirectoryDiffControl()
 
 		#region Public Events
 
-		public event EventHandler RecompareNeeded;
+		public event EventHandler? RecompareNeeded;
 
-		public event EventHandler<DifferenceEventArgs> ShowFileDifferences;
+		public event EventHandler<DifferenceEventArgs>? ShowFileDifferences;
 
 		#endregion
 
@@ -58,7 +58,7 @@ public bool CanShowDifferences
 		{
 			get
 			{
-				DirectoryDiffEntry entry = this.SelectedEntry;
+				DirectoryDiffEntry? entry = this.SelectedEntry;
 				bool result = entry != null && entry.IsFile && entry.InA && entry.InB && this.ShowFileDifferences != null;
 				return result;
 			}
@@ -134,12 +134,12 @@ public bool ShowToolBar
 
 		#region Private Properties
 
-		private DirectoryDiffEntry SelectedEntry
+		private DirectoryDiffEntry? SelectedEntry
 		{
 			get
 			{
 				TreeNode selectedNode = this.TreeB.Focused ? this.TreeB.SelectedNode : this.TreeA.SelectedNode;
-				DirectoryDiffEntry result = DirectoryDiffTreeView.GetEntryForNode(selectedNode);
+				DirectoryDiffEntry? result = DirectoryDiffTreeView.GetEntryForNode(selectedNode);
 				return result;
 			}
 		}
@@ -154,7 +154,7 @@ public bool Recompare()
 
 			if (this.CanRecompare)
 			{
-				this.RecompareNeeded(this, EventArgs.Empty);
+				this.RecompareNeeded?.Invoke(this, EventArgs.Empty);
 				result = true;
 			}
 
@@ -192,13 +192,18 @@ public void ShowDifferences()
 		{
 			if (this.CanShowDifferences)
 			{
-				DirectoryDiffEntry entry = this.SelectedEntry;
-
-				GetNodes(entry, out TreeNode nodeA, out TreeNode nodeB);
-				string fileA = this.TreeA.GetFullNameForNode(nodeA);
-				string fileB = this.TreeB.GetFullNameForNode(nodeB);
+				DirectoryDiffEntry? entry = this.SelectedEntry;
+				if (entry != null)
+				{
+					GetNodes(entry, out TreeNode? nodeA, out TreeNode? nodeB);
+					if (nodeA != null && nodeB != null)
+					{
+						string fileA = this.TreeA.GetFullNameForNode(nodeA);
+						string fileB = this.TreeB.GetFullNameForNode(nodeB);
 
-				this.ShowFileDifferences(this, new DifferenceEventArgs(fileA, fileB));
+						this.ShowFileDifferences?.Invoke(this, new DifferenceEventArgs(fileA, fileB));
+					}
+				}
 			}
 		}
 
@@ -214,10 +219,10 @@ public void View()
 
 		#region Private Methods
 
-		private static void GetNodes(DirectoryDiffEntry entry, out TreeNode nodeA, out TreeNode nodeB)
+		private static void GetNodes(DirectoryDiffEntry entry, out TreeNode? nodeA, out TreeNode? nodeB)
 		{
-			nodeA = (TreeNode)entry.TagA;
-			nodeB = (TreeNode)entry.TagB;
+			nodeA = (TreeNode?)entry.TagA;
+			nodeB = (TreeNode?)entry.TagB;
 		}
 
 		private static bool IsScrollingKey(KeyEventArgs e)
@@ -242,43 +247,43 @@ private static bool IsScrollingKey(KeyEventArgs e)
 			return result;
 		}
 
-		private void Recompare_Click(object sender, EventArgs e)
+		private void Recompare_Click(object? sender, EventArgs e)
 		{
 			this.Recompare();
 		}
 
-		private void ShowDifferences_Click(object sender, EventArgs e)
+		private void ShowDifferences_Click(object? sender, EventArgs e)
 		{
 			this.ShowDifferences();
 		}
 
-		private void View_Click(object sender, EventArgs e)
+		private void View_Click(object? sender, EventArgs e)
 		{
 			this.View();
 		}
 
 		[SuppressMessage("Design", "CC0091:Use static method", Justification = "Windows Forms designer prefers non-static.")]
-		private void ColorLegend_Paint(object sender, PaintEventArgs e)
+		private void ColorLegend_Paint(object? sender, PaintEventArgs e)
 		{
 			DiffControl.PaintColorLegendItem(sender as ToolStripItem, e);
 		}
 
-		private void DiffOptionsChanged(object sender, EventArgs e)
+		private void DiffOptionsChanged(object? sender, EventArgs e)
 		{
 			this.UpdateColors();
 		}
 
-		private void DirDiffControl_SizeChanged(object sender, EventArgs e)
+		private void DirDiffControl_SizeChanged(object? sender, EventArgs e)
 		{
 			this.pnlLeft.Width = (this.Width - this.Splitter.Width) / 2;
 		}
 
 		private void SyncTreeViewScrollPositions(DirectoryDiffTreeView source)
 		{
-			DirectoryDiffEntry entry = DirectoryDiffTreeView.GetEntryForNode(source.TopNode);
+			DirectoryDiffEntry? entry = DirectoryDiffTreeView.GetEntryForNode(source.TopNode);
 			if (entry != null)
 			{
-				GetNodes(entry, out TreeNode nodeA, out TreeNode nodeB);
+				GetNodes(entry, out TreeNode? nodeA, out TreeNode? nodeB);
 				if (nodeA != null && nodeB != null)
 				{
 					this.TreeA.TopNode = nodeA;
@@ -308,12 +313,12 @@ private void TreeA_KeyDown(object sender, KeyEventArgs e)
 			}
 		}
 
-		private void TreeA_MouseWheelMsg(object sender, EventArgs e)
+		private void TreeA_MouseWheelMsg(object? sender, EventArgs e)
 		{
 			this.SyncTreeViewScrollPositions(this.TreeA);
 		}
 
-		private void TreeA_VScroll(object sender, EventArgs e)
+		private void TreeA_VScroll(object? sender, EventArgs e)
 		{
 			this.SyncTreeViewScrollPositions(this.TreeA);
 		}
@@ -327,22 +332,22 @@ private void TreeB_KeyDown(object sender, KeyEventArgs e)
 			}
 		}
 
-		private void TreeB_MouseWheelMsg(object sender, EventArgs e)
+		private void TreeB_MouseWheelMsg(object? sender, EventArgs e)
 		{
 			this.SyncTreeViewScrollPositions(this.TreeB);
 		}
 
-		private void TreeB_VScroll(object sender, EventArgs e)
+		private void TreeB_VScroll(object? sender, EventArgs e)
 		{
 			this.SyncTreeViewScrollPositions(this.TreeB);
 		}
 
 		private void TreeNode_SelectChanged(object sender, TreeViewEventArgs e)
 		{
-			DirectoryDiffEntry entry = DirectoryDiffTreeView.GetEntryForNode(e.Node);
+			DirectoryDiffEntry? entry = DirectoryDiffTreeView.GetEntryForNode(e.Node);
 			if (entry != null)
 			{
-				GetNodes(entry, out TreeNode nodeA, out TreeNode nodeB);
+				GetNodes(entry, out TreeNode? nodeA, out TreeNode? nodeB);
 				if (nodeA != null && nodeB != null)
 				{
 					this.TreeA.SelectedNode = nodeA;
@@ -356,10 +361,10 @@ private void TreeNode_SelectChanged(object sender, TreeViewEventArgs e)
 		[SuppressMessage("Design", "CC0091:Use static method", Justification = "Windows Forms designer prefers non-static.")]
 		private void TreeNode_StateChange(object sender, TreeViewEventArgs e)
 		{
-			DirectoryDiffEntry entry = DirectoryDiffTreeView.GetEntryForNode(e.Node);
+			DirectoryDiffEntry? entry = DirectoryDiffTreeView.GetEntryForNode(e.Node);
 			if (entry != null)
 			{
-				GetNodes(entry, out TreeNode nodeA, out TreeNode nodeB);
+				GetNodes(entry, out TreeNode? nodeA, out TreeNode? nodeB);
 				if (nodeA != null && nodeB != null)
 				{
 					if (e.Action == TreeViewAction.Collapse)
@@ -394,14 +399,14 @@ private void TreeNode_StateChange(object sender, TreeViewEventArgs e)
 			}
 		}
 
-		private void TreeView_DoubleClick(object sender, EventArgs e)
+		private void TreeView_DoubleClick(object? sender, EventArgs e)
 		{
 			this.ShowDifferences();
 		}
 
-		private void TreeView_Enter(object sender, EventArgs e)
+		private void TreeView_Enter(object? sender, EventArgs e)
 		{
-			this.activeTree = (DirectoryDiffTreeView)sender;
+			this.activeTree = (DirectoryDiffTreeView)sender!;
 			this.UpdateButtons();
 		}
 
diff --git a/src/Menees.Diffs.Windows.Forms/DirectoryDiffTreeView.cs b/src/Menees.Diffs.Windows.Forms/DirectoryDiffTreeView.cs
index c7a61e4..94b4c0c 100644
--- a/src/Menees.Diffs.Windows.Forms/DirectoryDiffTreeView.cs
+++ b/src/Menees.Diffs.Windows.Forms/DirectoryDiffTreeView.cs
@@ -24,7 +24,7 @@ internal sealed class DirectoryDiffTreeView : TreeView
 		private const int FolderOpenIndex = 1;
 
 		private bool useA;
-		private DirectoryDiffResults results;
+		private DirectoryDiffResults? results;
 
 		#endregion
 
@@ -43,9 +43,9 @@ public DirectoryDiffTreeView()
 
 		#region Internal Events
 
-		internal event EventHandler MouseWheelMsg;
+		internal event EventHandler? MouseWheelMsg;
 
-		internal event EventHandler VScroll;
+		internal event EventHandler? VScroll;
 
 		#endregion
 
@@ -60,7 +60,7 @@ public bool CanView
 				TreeNode node = this.SelectedNode;
 				if (node != null)
 				{
-					DirectoryDiffEntry entry = GetEntryForNode(node);
+					DirectoryDiffEntry? entry = GetEntryForNode(node);
 					if (entry != null)
 					{
 						result = (this.useA && entry.InA) || (!this.useA && entry.InB);
@@ -75,18 +75,23 @@ public bool CanView
 
 		#region Public Methods
 
-		public static DirectoryDiffEntry GetEntryForNode(TreeNode node) => node?.Tag as DirectoryDiffEntry;
+		public static DirectoryDiffEntry? GetEntryForNode(TreeNode? node) => node?.Tag as DirectoryDiffEntry;
 
 		public string GetFullNameForNode(TreeNode node)
 		{
-			string nodePath = node.FullPath;
-			string basePath = this.useA ? this.results.DirectoryA.FullName : this.results.DirectoryB.FullName;
-			if (!basePath.EndsWith("\\"))
+			string result = node.FullPath;
+			if (this.results != null)
 			{
-				basePath += "\\";
+				string basePath = this.useA ? this.results.DirectoryA.FullName : this.results.DirectoryB.FullName;
+				if (!basePath.EndsWith("\\"))
+				{
+					basePath += "\\";
+				}
+
+				result = basePath + result;
 			}
 
-			return basePath + nodePath;
+			return result;
 		}
 
 		public void SetData(DirectoryDiffResults results, bool useA)
@@ -122,13 +127,25 @@ protected override void Dispose(bool disposing)
 
 		protected override void OnAfterCollapse(TreeViewEventArgs e)
 		{
-			this.SetNodeImage(e.Node, GetEntryForNode(e.Node));
+			TreeNode? node = e.Node;
+			DirectoryDiffEntry? entry = GetEntryForNode(node);
+			if (node != null && entry != null)
+			{
+				this.SetNodeImage(node, entry);
+			}
+
 			base.OnAfterCollapse(e);
 		}
 
 		protected override void OnAfterExpand(TreeViewEventArgs e)
 		{
-			this.SetNodeImage(e.Node, GetEntryForNode(e.Node));
+			TreeNode? node = e.Node;
+			DirectoryDiffEntry? entry = GetEntryForNode(node);
+			if (node != null && entry != null)
+			{
+				this.SetNodeImage(node, entry);
+			}
+
 			base.OnAfterExpand(e);
 		}
 
@@ -161,7 +178,7 @@ protected override void WndProc(ref Message m)
 
 		#region Private Methods
 
-		private void AddEntry(DirectoryDiffEntry entry, TreeNode parentNode)
+		private void AddEntry(DirectoryDiffEntry entry, TreeNode? parentNode)
 		{
 			TreeNode node = new()
 			{
@@ -194,14 +211,14 @@ private void AddEntry(DirectoryDiffEntry entry, TreeNode parentNode)
 
 			if (!entry.IsFile)
 			{
-				foreach (DirectoryDiffEntry subEntry in entry.Subentries)
+				foreach (DirectoryDiffEntry subEntry in entry.Subentries!)
 				{
 					this.AddEntry(subEntry, node);
 				}
 			}
 		}
 
-		private void DiffOptionsChanged(object sender, EventArgs e)
+		private void DiffOptionsChanged(object? sender, EventArgs e)
 		{
 			this.SetNodesColors(this.Nodes);
 		}
@@ -213,9 +230,12 @@ private void PopulateTree()
 			{
 				this.Nodes.Clear();
 
-				foreach (DirectoryDiffEntry entry in this.results.Entries)
+				if (this.results != null)
 				{
-					this.AddEntry(entry, null);
+					foreach (DirectoryDiffEntry entry in this.results.Entries)
+					{
+						this.AddEntry(entry, null);
+					}
 				}
 
 				this.ExpandAll();
@@ -280,7 +300,7 @@ private void SetNodeImage(TreeNode node, DirectoryDiffEntry entry)
 				//
 				// Also, we should only show a folder open if we're
 				// showing recursive differences.
-				if (this.results.Recursive && node.IsExpanded && entry.InA && entry.InB)
+				if (this.results != null && this.results.Recursive && node.IsExpanded && entry.InA && entry.InB)
 				{
 					index = FolderOpenIndex;
 				}
@@ -302,7 +322,12 @@ private void SetNodesColors(TreeNodeCollection nodes)
 		{
 			foreach (TreeNode node in nodes)
 			{
-				this.SetNodeColor(node, GetEntryForNode(node));
+				DirectoryDiffEntry? entry = GetEntryForNode(node);
+				if (entry != null)
+				{
+					this.SetNodeColor(node, entry);
+				}
+
 				this.SetNodesColors(node.Nodes);
 			}
 		}
diff --git a/src/Menees.Diffs.Windows.Forms/Menees.Diffs.Windows.Forms.csproj b/src/Menees.Diffs.Windows.Forms/Menees.Diffs.Windows.Forms.csproj
index 2d8a1fd..2126275 100644
--- a/src/Menees.Diffs.Windows.Forms/Menees.Diffs.Windows.Forms.csproj
+++ b/src/Menees.Diffs.Windows.Forms/Menees.Diffs.Windows.Forms.csproj
@@ -1,10 +1,11 @@
-<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">
+<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">
 
 	<PropertyGroup>
 		<TargetFrameworks>$(MeneesTargetNetCoreWindows);$(MeneesTargetNetFramework)</TargetFrameworks>
 		<GeneratePackageOnBuild>true</GeneratePackageOnBuild>
 		<UseWindowsForms>true</UseWindowsForms>
 		<Description>Windows Forms controls for showing diffs of text, files, and directories</Description>
+		<Nullable>enable</Nullable>
 	</PropertyGroup>
 
 	<ItemGroup>
@@ -27,4 +28,9 @@
 		</EmbeddedResource>
 	</ItemGroup>
 
+	<PropertyGroup Condition=" '$(TargetFramework)' == '$(MeneesTargetNetFramework)' ">
+		<!-- Disable IDE0079 (Remove unnecessary suppressions) warning because we have suppressions required by $(MeneesTargetNetCoreWindows). -->
+		<NoWarn>IDE0079</NoWarn>
+	</PropertyGroup>
+
 </Project>