diff --git a/.devcontainer/devcontainer.json b/.devcontainer/devcontainer.json
new file mode 100644
index 0000000..66e6675
--- /dev/null
+++ b/.devcontainer/devcontainer.json
@@ -0,0 +1,8 @@
+{
+    "image":"mcr.microsoft.com/vscode/devcontainers/base:ubuntu",
+    "features": {
+        "ghcr.io/shyim/devcontainers-features/php:0": {
+            "extensionsExtra": "intl mysqli mbstring"
+        }
+    }
+}
diff --git a/phpcs.xml.dist b/phpcs.xml.dist
new file mode 100644
index 0000000..0d5d7c8
--- /dev/null
+++ b/phpcs.xml.dist
@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ruleset name="SilverStripe">
+    <description>CodeSniffer ruleset for SilverStripe coding conventions.</description>
+
+    <file>src</file>
+
+    <!-- base rules are PSR-2 -->
+    <rule ref="PSR2" >
+        <!-- Current exclusions -->
+        <exclude name="PSR1.Methods.CamelCapsMethodName" />
+        <exclude name="PSR1.Files.SideEffects.FoundWithSymbols" />
+        <exclude name="PSR2.Classes.PropertyDeclaration" />
+        <exclude name="PSR2.ControlStructures.SwitchDeclaration" /> <!-- causes php notice while linting -->
+        <exclude name="PSR2.ControlStructures.SwitchDeclaration.WrongOpenercase" />
+        <exclude name="PSR2.ControlStructures.SwitchDeclaration.WrongOpenerdefault" />
+        <exclude name="PSR2.ControlStructures.SwitchDeclaration.TerminatingComment" />
+        <exclude name="PSR2.Methods.MethodDeclaration.Underscore" />
+        <exclude name="Squiz.Scope.MethodScope" />
+        <exclude name="Squiz.Classes.ValidClassName.NotCamelCaps" />
+        <exclude name="Generic.Files.LineLength.TooLong" />
+        <exclude name="PEAR.Functions.ValidDefaultValue.NotAtEnd" />
+    </rule>
+    <rule ref="Squiz.Strings.ConcatenationSpacing">
+        <properties>
+            <property name="spacing" value="1" />
+            <property name="ignoreNewlines" value="true"/>
+        </properties>
+    </rule>
+
+    <!-- include php files only -->
+    <arg name="extensions" value="php,lib,inc,php5"/>
+</ruleset>
diff --git a/src/DropzoneFile.php b/src/DropzoneFile.php
index 8eb98fd..3086c94 100644
--- a/src/DropzoneFile.php
+++ b/src/DropzoneFile.php
@@ -41,32 +41,33 @@ public function IsImage()
      */
     public function getPreviewThumbnail($w = null, $h = null)
     {
-        if(!$w) { $w = $this->owner->config()->grid_thumbnail_width;
+        if (!$w) {
+            $w = $this->owner->config()->grid_thumbnail_width;
         }
-        if(!$h) { $h = $this->owner->config()->grid_thumbnail_height;
+        if (!$h) {
+            $h = $this->owner->config()->grid_thumbnail_height;
         }
 
-        if($this->IsImage() && Director::fileExists($this->owner->Filename)) {
+        if ($this->IsImage() && Director::fileExists($this->owner->Filename)) {
             return $this->owner->CroppedImage($w, $h);
         }
 
-        $sizes = Config::inst()->forClass(FileAttachmentField::class)->icon_sizes;
+        $sizes = Config::forClass(FileAttachmentField::class)->icon_sizes;
         sort($sizes);
 
-        foreach($sizes as $size) {
-            if($w <= $size) {
-                if($this->owner instanceof Folder) {
+        foreach ($sizes as $size) {
+            if ($w <= $size) {
+                if ($this->owner instanceof Folder) {
                     $file = $this->getFilenameForType('_folder', $size);
-                }
-                else {
+                } else {
                     $file = $this->getFilenameForType($this->owner->getExtension(), $size);
                 }
-                if(!file_exists(BASE_PATH.'/'.$file)) {
+                if (!file_exists(BASE_PATH . '/' . $file)) {
                     $file = $this->getFilenameForType('_blank', $size);
                 }
 
                 $image = Image::create();
-                $image->setFromLocalFile(Director::getAbsFile($file), basename($file));
+                $image->setFromLocalFile(Director::getAbsFile($file), basename($file ?? ''));
 
                 return $image;
             }
@@ -86,7 +87,7 @@ protected function getFilenameForType($ext, $size)
         return ModuleResourceLoader::singleton()->resolveURL(sprintf(
             'unclecheese/dropzone:images/file-icons/%spx/%s.png',
             $size,
-            strtolower($ext)
+            strtolower($ext ?? '')
         ));
     }
-}
\ No newline at end of file
+}
diff --git a/src/FileAttachmentField.php b/src/FileAttachmentField.php
index ddea293..cd73edc 100644
--- a/src/FileAttachmentField.php
+++ b/src/FileAttachmentField.php
@@ -2,6 +2,7 @@
 
 namespace UncleCheese\Dropzone;
 
+use Exception;
 use SilverStripe\Core\Manifest\ModuleLoader;
 use SilverStripe\Core\Manifest\ModuleManifest;
 use SilverStripe\Core\Manifest\ModuleResourceLoader;
@@ -39,15 +40,15 @@ class FileAttachmentField extends FileField
      *
      * @var array
      */
-    private static $allowed_actions = array (
+    private static $allowed_actions =  [
         'upload',
         'handleSelect',
-    );
+    ];
 
 
-    private static $url_handlers = array (
+    private static $url_handlers =  [
         'select' => 'handleSelect',
-    );
+    ];
 
     /**
      * Track files that are uploaded and remove the tracked files when
@@ -130,9 +131,11 @@ class FileAttachmentField extends FileField
     public static function camelise($str)
     {
         return preg_replace_callback(
-            '/_([a-z])/', function ($c) {
+            '/_([a-z])/',
+            function ($c) {
                 return strtoupper($c[1]);
-            }, $str
+            },
+            $str ?? ''
         );
     }
 
@@ -144,12 +147,17 @@ public static function camelise($str)
      */
     public static function underscorise($str)
     {
+        if (!is_string($str)) {
+            return '';
+        }
         $str[0] = strtolower($str[0]);
 
         return preg_replace_callback(
-            '/([A-Z])/', function ($c) {
+            '/([A-Z])/',
+            function ($c) {
                 return "_" . strtolower($c[1]);
-            }, $str
+            },
+            $str
         );
     }
 
@@ -162,10 +170,10 @@ public static function underscorise($str)
     public static function get_filesize_from_ini()
     {
         $bytes = min(
-            array(
-            File::ini2bytes(ini_get('post_max_size') ?: '8M'),
-            File::ini2bytes(ini_get('upload_max_filesize') ?: '2M')
-            )
+            [
+                Convert::memstring2bytes(ini_get('post_max_size') ?: '8M'),
+                Convert::memstring2bytes(ini_get('upload_max_filesize') ?: '2M')
+            ]
         );
 
         return floor($bytes/(1024*1024));
@@ -205,7 +213,7 @@ public function __construct($name, $title = null, $value = null, $form = null)
      * @param  array $attributes
      * @return SSViewer
      */
-    public function FieldHolder($attributes = array ())
+    public function FieldHolder($attributes = [])
     {
         $this->defineFieldHolderRequirements();
         return parent::FieldHolder($attributes);
@@ -218,7 +226,7 @@ public function FieldHolder($attributes = array ())
      * @param  array $attributes
      * @return SSViewer
      */
-    public function SmallFieldHolder($attributes = array ())
+    public function SmallFieldHolder($attributes = [])
     {
         $this->defineFieldHolderRequirements();
         return parent::SmallFieldHolder($attributes);
@@ -231,16 +239,16 @@ protected function defineFieldHolderRequirements()
     {
         Requirements::javascript('unclecheese/dropzone:javascript/dropzone.js');
         Requirements::javascript('unclecheese/dropzone:javascript/file_attachment_field.js');
-        if($this->isCMS()) {
+        if ($this->isCMS()) {
             Requirements::javascript('unclecheese/dropzone:javascript/file_attachment_field_backend.js');
         }
         Requirements::css('unclecheese/dropzone:css/file_attachment_field.css');
 
-        if(!$this->getSetting('url')) {
+        if (!$this->getSetting('url')) {
             $this->settings['url'] = $this->Link('upload');
         }
 
-        if(!$this->getSetting('maxFilesize')) {
+        if (!$this->getSetting('maxFilesize')) {
             $this->settings['maxFilesize'] = static::get_filesize_from_ini();
         }
         // The user may not have opted into a multiple upload. If the form field
@@ -248,8 +256,8 @@ protected function defineFieldHolderRequirements()
         $this->settings['uploadMultiple'] = $this->IsMultiple();
 
         // Auto filter images if assigned to an Image relation
-        if($class = $this->getFileClass()) {
-            if(Injector::inst()->get($class) instanceof Image) {
+        if ($class = $this->getFileClass()) {
+            if (Injector::inst()->get($class) instanceof Image) {
                 $this->imagesOnly();
             }
         }
@@ -264,26 +272,28 @@ protected function defineFieldHolderRequirements()
     public function saveInto(DataObjectInterface $record)
     {
         $fieldname = $this->getName();
-        if(!$fieldname) { return $this;
+        if (!$fieldname) {
+            return $this;
         }
 
         // Handle deletions. This is a bit of a hack. A workaround for having a single form field
         // post two params.
-        $deletions = Controller::curr()->getRequest()->postVar('__deletion__'.$this->getName());
+        $deletions = Controller::curr()->getRequest()->postVar('__deletion__' . $this->getName());
 
         if ($deletions && is_array($deletions)) {
-            foreach($deletions as $id) {
+            foreach ($deletions as $id) {
                 $this->deleteFileByID($id);
             }
         }
 
+        /** @var DataObject $record */
         $ones = $record->hasOne();
 
-        if(($relation = $this->getRelation($record))) {
+        if (($relation = $this->getRelation($record))) {
             $relation->setByIDList($this->Value());
-        } else if(isset($ones[$fieldname])) {
+        } elseif (isset($ones[$fieldname])) {
             $record->{"{$fieldname}ID"} = $this->Value() ?: 0;
-        } elseif($record->hasField($fieldname)) {
+        } elseif ($record->hasField($fieldname)) {
             $record->$fieldname = is_array($this->Value()) ? implode(',', $this->Value()) : $this->Value();
         }
 
@@ -371,7 +381,7 @@ public function setMaxFilesize($num)
         $this->settings['maxFilesize'] = $num;
         $validator = $this->getValidator();
         if ($validator) {
-            $validator->setAllowedMaxFileSize($num.'m');
+            $validator->setAllowedMaxFileSize($num . 'm');
         }
         return $this;
     }
@@ -452,7 +462,7 @@ public function addValidFileIDs(array $ids)
         $validIDs = $session->get('FileAttachmentField.validFileIDs');
 
         if (!$validIDs) {
-            $validIDs = array();
+            $validIDs = [];
         }
         foreach ($ids as $id) {
             $validIDs[$id] = $id;
@@ -511,7 +521,7 @@ public function validate($validator)
                 "validation"
             );
             $result = false;
-        } else if ($value && is_array($value)) {
+        } elseif ($value && is_array($value)) {
             // Prevent a malicious user from inspecting element and changing
             // one of the <input type="hidden"> fields to use an invalid File ID.
             $validIDs = $this->getValidFileIDs();
@@ -524,7 +534,7 @@ public function validate($validator)
                             _t(
                                 'FileAttachmentField.VALIDATION',
                                 'Invalid file ID sent %s.',
-                                array('id' => $id)
+                                ['id' => $id]
                             ),
                             "validation"
                         );
@@ -542,26 +552,26 @@ public function validate($validator)
      * @param  array|DataObject $data
      * @return $this
      */
-    public function setValue($val, $data = array())
+    public function setValue($val, $data = [])
     {
         if (!$val && $data && $data instanceof DataObject && $data->exists()) {
             // NOTE: This stops validation errors from occuring when editing
             //       an already saved DataObject.
             $fieldName = $this->getName();
-            $ids = array();
+            $ids = [];
             if ($data->getSchema()->hasOneComponent(get_class($data), $fieldName)) {
-                $id = $data->{$fieldName.'ID'};
+                $id = $data->{$fieldName . 'ID'};
                 if ($id) {
-                    $ids[] = $id; 
+                    $ids[] = $id;
                 }
-            } else if ($data->getSchema()->hasManyComponent(get_class($data), $fieldName) || $data->getSchema()->manyManyComponent(get_class($data), $fieldName)) {
+            } elseif ($data->getSchema()->hasManyComponent(get_class($data), $fieldName) || $data->getSchema()->manyManyComponent(get_class($data), $fieldName)) {
                 $files = $data->{$fieldName}();
                 if ($files) {
                     foreach ($files as $file) {
                         if (!$file->exists()) {
                             continue;
                         }
-                        $ids[] = $file->ID; 
+                        $ids[] = $file->ID;
                     }
                 }
             }
@@ -630,7 +640,7 @@ public function setThumbnailHeight($num)
      */
     public function setView($view)
     {
-        if(!in_array($view, array ('grid','list'))) {
+        if (!in_array($view, ['grid','list'])) {
             throw new Exception("FileAttachmentField::setView - View must be one of 'grid' or 'list'");
         }
 
@@ -669,12 +679,12 @@ public function setClickable($val)
      * @param  array $files
      * @return FileAttachmentField
      */
-    public function setAcceptedFiles($files = array ())
+    public function setAcceptedFiles($files = [])
     {
-        if(is_array($files)) {
+        if (is_array($files)) {
             $files = implode(',', $files);
         }
-        $files = str_replace(' ', '', $files);
+        $files = str_replace(' ', '', $files ?? '');
         $this->settings['acceptedFiles'] = $files;
 
         // Update validator
@@ -682,7 +692,7 @@ public function setAcceptedFiles($files = array ())
         if ($validator) {
             $fileExts = explode(',', $files);
 
-            $validatorExts = array();
+            $validatorExts = [];
             foreach ($fileExts as $fileExt) {
                 if ($fileExt && isset($fileExt[0]) && $fileExt[0] === '.') {
                     $fileExt = substr($fileExt, 1);
@@ -702,7 +712,7 @@ public function setAcceptedFiles($files = array ())
      */
     public function imagesOnly()
     {
-        $this->setAcceptedFiles(array('.png','.gif','.jpeg','.jpg'));
+        $this->setAcceptedFiles(['.png','.gif','.jpeg','.jpg']);
 
         return $this;
     }
@@ -713,9 +723,9 @@ public function imagesOnly()
      * @param  array $types
      * @return FileAttachmentField
      */
-    public function setAcceptedMimeTypes($types = array ())
+    public function setAcceptedMimeTypes($types = [])
     {
-        if(is_array($types)) {
+        if (is_array($types)) {
             $types = implode(',', $types);
         }
         $this->settings['acceptedMimeTypes'] = $types;
@@ -809,8 +819,8 @@ public function addParam($key, $val)
      */
     public function setPermissions($perms)
     {
-        foreach($perms as $perm => $val) {
-            if(!isset($this->permissions[$perm])) {
+        foreach ($perms as $perm => $val) {
+            if (!isset($this->permissions[$perm])) {
                 throw new Exception("FileAttachmentField::setPermissions - Permission $perm is not allowed");
             }
             $this->permissions[$perm] = $val;
@@ -830,9 +840,9 @@ public function setPermissions($perms)
     public function setPermission($perm, $val)
     {
         return $this->setPermissions(
-            array(
+            [
             $perm => $val
-            )
+            ]
         );
     }
 
@@ -862,7 +872,7 @@ public function isCMS()
     {
         return Controller::curr() instanceof LeftAndMain;
     }
-    
+
     /**
      * @note   these are user-friendlier versions of internal PHP errors reported back in the ['error'] value of an upload
      * @return string
@@ -870,29 +880,29 @@ public function isCMS()
     private function getUploadUserError($code)
     {
         $error_message = "";
-        switch($code) {
-        case UPLOAD_ERR_OK:
-            // no error - 0
+        switch ($code) {
+            case UPLOAD_ERR_OK:
+                // no error - 0
             return "";
-          break;
-        case UPLOAD_ERR_INI_SIZE:
-        case UPLOAD_ERR_FORM_SIZE:
-            $error_message = _t('FileAttachmentField.ERRFILESIZE', 'The file is too large, please try again with a smaller version of the file.');
             break;
-        case UPLOAD_ERR_PARTIAL:
-            $error_message = _t('FileAttachmentField.ERRPARTIALUPLOAD', 'The file was only partially uploaded, did you cancel the upload? Please try again.');
+            case UPLOAD_ERR_INI_SIZE:
+            case UPLOAD_ERR_FORM_SIZE:
+                $error_message = _t('FileAttachmentField.ERRFILESIZE', 'The file is too large, please try again with a smaller version of the file.');
             break;
-        case UPLOAD_ERR_NO_FILE:
-            $error_message = _t('FileAttachmentField.ERRNOFILE', 'No file upload was detected.');
+            case UPLOAD_ERR_PARTIAL:
+                $error_message = _t('FileAttachmentField.ERRPARTIALUPLOAD', 'The file was only partially uploaded, did you cancel the upload? Please try again.');
             break;
-        case UPLOAD_ERR_NO_TMP_DIR:
-        case UPLOAD_ERR_CANT_WRITE:
-        case UPLOAD_ERR_EXTENSION:
-            $error_message = _t('FileAttachmentField.ERRSYSTEMFAIL', 'Sorry, the system is not allowing file uploads at this time.');
+            case UPLOAD_ERR_NO_FILE:
+                $error_message = _t('FileAttachmentField.ERRNOFILE', 'No file upload was detected.');
             break;
-        default:
-            // handles if an extra error value is added at some point as a general error
-            $error_message = _t('FileAttachmentField.ERRUNKNOWNCODE', 'Sorry, an unknown error has occured. Please try again later.');
+            case UPLOAD_ERR_NO_TMP_DIR:
+            case UPLOAD_ERR_CANT_WRITE:
+            case UPLOAD_ERR_EXTENSION:
+                $error_message = _t('FileAttachmentField.ERRSYSTEMFAIL', 'Sorry, the system is not allowing file uploads at this time.');
+            break;
+            default:
+                // handles if an extra error value is added at some point as a general error
+                $error_message = _t('FileAttachmentField.ERRUNKNOWNCODE', 'Sorry, an unknown error has occured. Please try again later.');
             break;
         }
         return $error_message;
@@ -914,29 +924,29 @@ private function getUploadUserError($code)
      */
     public function upload(HTTPRequest $request)
     {
-      
+
         $name = $this->getSetting('paramName');
-        $files = (!empty($_FILES[$name]) ? $_FILES[$name] : array());
-        $tmpFiles = array();
+        $files = (!empty($_FILES[$name]) ? $_FILES[$name] : []);
+        $tmpFiles = [];
 
         // Checking if field is not supporting uploads
-        if($this->isDisabled() || $this->isReadonly() || !$this->CanUpload()) {
+        if ($this->isDisabled() || $this->isReadonly() || !$this->CanUpload()) {
             $error_message = _t('FileAttachmentField.UPLOADFORBIDDEN', 'Files cannot be uploaded via this form at the current time.');
             return $this->httpError(403, $error_message);
         }
-        
+
         // No files detected in the upload, this can occur if post_max_size is < the upload size
         $value = $request->postVar($name);
-        if(empty($files) || empty($value)) {
+        if (empty($files) || empty($value)) {
             $error_message = _t('FileAttachmentField.NOFILESUPLOADED', 'No files were detected in your upload. Please try again later.');
             return $this->httpError(400, $error_message);
         }
-        
+
         // Security token check, must go after above check as a low post_max_size can scrub the Security Token name from the request
         $form = $this->getForm();
-        if($form) {
+        if ($form) {
             $token = $form->getSecurityToken();
-            if(!$token->checkRequest($request)) {
+            if (!$token->checkRequest($request)) {
                 $error_message = _t('FileAttachmentField.BADSECURITYTOKEN', 'Your form session has expired, please reload the form and try again.');
                 return $this->httpError(400, $error_message);
             }
@@ -944,27 +954,26 @@ public function upload(HTTPRequest $request)
 
         // Sort the files out into a list of arrays containing each property
         // http://php.net/manual/en/features.file-upload.post-method.php
-        if(!empty($files['tmp_name']) && is_array($files['tmp_name'])) {
-            for($i = 0; $i < count($files['tmp_name']); $i++) {
-                $tmpFile = array();
-                foreach(array('name', 'type', 'tmp_name', 'error', 'size') as $field) {
+        if (!empty($files['tmp_name']) && is_array($files['tmp_name'])) {
+            for ($i = 0; $i < count($files['tmp_name']); $i++) {
+                $tmpFile = [];
+                foreach (['name', 'type', 'tmp_name', 'error', 'size'] as $field) {
                     $tmpFile[$field] = $files[$field][$i];
                 }
                 $tmpFiles[] = $tmpFile;
             }
-        }
-        elseif(!empty($files['tmp_name'])) {
+        } elseif (!empty($files['tmp_name'])) {
             $tmpFiles[] = $files;
         }
 
-        $ids = array ();
-        foreach($tmpFiles as $tmpFile) {
-            if($tmpFile['error']) {
+        $ids =  [];
+        foreach ($tmpFiles as $tmpFile) {
+            if ($tmpFile['error']) {
                 // http://php.net/manual/en/features.file-upload.errors.php
                 $user_message = $this->getUploadUserError($tmpFile['error']);
                 return $this->httpError(400, $user_message);
             }
-            if($relationClass = $this->getFileClass($tmpFile['name'])) {
+            if ($relationClass = $this->getFileClass($tmpFile['name'])) {
                 $fileObject = Injector::inst()->create($relationClass);
             }
 
@@ -992,7 +1001,7 @@ public function upload(HTTPRequest $request)
                     if (!$formController instanceof LeftAndMain) {
                         $trackFile->setRecord($formController->getRecord());
                     }
-                } else if ($formClass !== 'Form') {
+                } elseif ($formClass !== 'Form') {
                     $trackFile->ControllerClass = $formClass;
                 } else {
                     // If using generic 'Form' instance, get controller
@@ -1014,7 +1023,7 @@ public function upload(HTTPRequest $request)
      */
     public function handleSelect(HTTPRequest $request)
     {
-        if($this->isDisabled() || $this->isReadonly() || !$this->CanAttach()) {
+        if ($this->isDisabled() || $this->isReadonly() || !$this->CanAttach()) {
             return $this->httpError(403);
         }
 
@@ -1031,17 +1040,16 @@ public function handleSelect(HTTPRequest $request)
      */
     protected function deleteFileByID($id)
     {
-        if($this->CanDelete() && $record = $this->getRecord()) {
+        if ($this->CanDelete() && $record = $this->getRecord()) {
             $ones = $record->hasOne();
 
-            if($relation = $this->getRelation()) {
+            if ($relation = $this->getRelation()) {
                 $file = $relation->byID($id);
-            }
-            else if(isset($ones[$this->getName()])) {
+            } elseif (isset($ones[$this->getName()])) {
                 $file = $record->{$this->getName()}();
             }
 
-            if($file && $file->canDelete()) {
+            if ($file && $file->canDelete()) {
                 $file->delete();
 
                 return true;
@@ -1058,20 +1066,20 @@ protected function deleteFileByID($id)
      */
     public function IsMultiple()
     {
-        if($this->getSetting('uploadMultiple')) {
+        if ($this->getSetting('uploadMultiple')) {
             return true;
         }
 
-        if($record = $this->getRecord()) {
+        if ($record = $this->getRecord()) {
             $manyMany = $record->manyMany();
 
-            if(isset($manyMany[$this->getName()])) {
+            if (isset($manyMany[$this->getName()])) {
                 return true;
             }
 
             $hasMany = $record->hasMany();
 
-            if(isset($hasMany[$this->getName()])) {
+            if (isset($hasMany[$this->getName()])) {
                 return true;
             }
         }
@@ -1086,7 +1094,7 @@ public function IsMultiple()
      */
     public function InputName()
     {
-        return $this->IsMultiple() ? $this->getName()."[]" : $this->getName();
+        return $this->IsMultiple() ? $this->getName() . "[]" : $this->getName();
     }
 
     /**
@@ -1096,26 +1104,25 @@ public function InputName()
      */
     public function AttachedFiles()
     {
-        if($record = $this->getRecord()) {
-            if($record->hasMethod($this->getName())) {
+        if ($record = $this->getRecord()) {
+            if ($record->hasMethod($this->getName())) {
                 $result = $record->{$this->getName()}();
 
-                if($result instanceof SS_List) {
+                if ($result instanceof SS_List) {
                     return $result;
-                }
-                else if($result->exists()) {
-                    return ArrayList::create(array($result));
+                } elseif ($result->exists()) {
+                    return ArrayList::create([$result]);
                 }
             }
         }
 
         if ($ids = $this->dataValue()) {
-            if($ids instanceof ManyManyList) {
+            if ($ids instanceof ManyManyList) {
                 $ids = array_keys($ids->map()->toArray());
             }
 
             if (!is_array($ids)) {
-                $ids = explode(',', $ids);
+                $ids = explode(',', $ids ?? '');
             }
 
             $attachments = ArrayList::create();
@@ -1149,16 +1156,18 @@ public function RootThumbnailsDir()
      */
     public function ThumbnailsDir()
     {
-        return $this->RootThumbnailsDir().'/'.$this->TemplateThumbnailSize()."px";
+        return $this->RootThumbnailsDir() . '/' . $this->TemplateThumbnailSize() . "px";
     }
 
 
     public function CSSSize()
     {
         $w = $this->getSelectedThumbnailWidth();
-        if($w < 150) { return "small";
+        if ($w < 150) {
+            return "small";
         }
-        if($w < 250) { return "medium";
+        if ($w < 250) {
+            return "medium";
         }
 
         return "large";
@@ -1234,7 +1243,6 @@ public function CanAttach()
     public function PreviewTemplate($fileID = null)
     {
         return $this->renderWith($this->previewTemplate);
-
     }
 
     /**
@@ -1247,8 +1255,9 @@ public function TemplateThumbnailSize()
     {
         $w = $this->getSelectedThumbnailWidth();
 
-        foreach($this->config()->icon_sizes as $size) {
-            if($w <= $size) { return $size;
+        foreach ($this->config()->icon_sizes as $size) {
+            if ($w <= $size) {
+                return $size;
             }
         }
     }
@@ -1273,10 +1282,11 @@ public function AutoProcess()
      */
     protected function checkPerm($perm)
     {
-        if(!isset($this->permissions[$perm])) { return false;
+        if (!isset($this->permissions[$perm])) {
+            return false;
         }
 
-        if(is_callable($this->permissions[$perm])) {
+        if (is_callable($this->permissions[$perm])) {
             return $this->permissions[$perm]();
         }
 
@@ -1298,22 +1308,23 @@ public function getFileClass($filename = null)
         $name = $this->getName();
         $record = $this->getRecord();
 
-        $ext = pathinfo($filename, PATHINFO_EXTENSION);
+        $ext = pathinfo($filename ?? '', PATHINFO_EXTENSION);
         $defaultClass = File::get_class_for_file_extension($ext);
 
-        if(empty($name) || empty($record)) {
+        if (empty($name) || empty($record)) {
             return $defaultClass;
         }
 
-        if($record) {
+        if ($record) {
             $class = $record->getRelationClass($name);
-            if(!$class) { $class = File::class;
+            if (!$class) {
+                $class = File::class;
             }
         }
 
-        if($filename) {
-            if($defaultClass == "Image" 
-                && $this->config()->upgrade_images 
+        if ($filename) {
+            if ($defaultClass == "Image"
+                && $this->config()->upgrade_images
                 && !Injector::inst()->get($class) instanceof Image
             ) {
                 $class = Image::class;
@@ -1334,16 +1345,15 @@ public function getRecord()
             $record = $this->form->getRecord();
             if ($record && $record instanceof DataObject) {
                 $this->record = $record;
-            }
-            else if ($controller = $this->form->getController()) {
-                if($controller->hasMethod('data')
+            } elseif ($controller = $this->form->getController()) {
+                if ($controller->hasMethod('data')
                     && ($record = $controller->data())
                     && ($record instanceof DataObject)
                 ) {
                     $this->record = $record;
-                } else if($controller->hasMethod('getRecord')) {
-                    if($controller->hasMethod('currentPageID')) {
-                        if($record = $controller->getRecord($controller->currentPageID())) {
+                } elseif ($controller->hasMethod('getRecord')) {
+                    if ($controller->hasMethod('currentPageID')) {
+                        if ($record = $controller->getRecord($controller->currentPageID())) {
                             $this->record = $record;
                         }
                     } else {
@@ -1359,14 +1369,15 @@ public function getRecord()
     /**
      * Gets the name of the relation, if attached to a record
      *
-     * @return string
+     * @return RelationList|UnsavedRelationList|bool
      */
     protected function getRelation($record = null)
     {
-        if(!$record) { $record = $this->getRecord();
+        if (!$record) {
+            $record = $this->getRecord();
         }
 
-        if($record) {
+        if ($record) {
             $fieldname = $this->getName();
             $relation = $record->hasMethod($fieldname) ? $record->$fieldname() : null;
 
@@ -1386,7 +1397,7 @@ protected function getRelation($record = null)
      */
     protected function getSetting($setting)
     {
-        if(isset($this->settings[$setting])) {
+        if (isset($this->settings[$setting])) {
             return $this->settings[$setting];
         }
 
@@ -1407,11 +1418,11 @@ protected function getDefaults()
         $file_path = ModuleLoader::inst()->getManifest()->getModule('unclecheese/dropzone')
             ->getResource($this->config()->default_config_path)
             ->getPath();
-        if(!file_exists($file_path)) {
+        if (!file_exists($file_path)) {
             throw new Exception("FileAttachmentField::getDefaults() - There is no config json file at $file_path");
         }
 
-        return Convert::json2array(file_get_contents($file_path));
+        return json_decode(file_get_contents($file_path) ?? '', true);
     }
 
     /**
@@ -1421,7 +1432,7 @@ protected function getDefaults()
      */
     public function getSelectedThumbnailWidth()
     {
-        if($w = $this->getSetting('thumbnailWidth')) {
+        if ($w = $this->getSetting('thumbnailWidth')) {
             return $w;
         }
 
@@ -1437,7 +1448,7 @@ public function getSelectedThumbnailWidth()
      */
     public function getSelectedThumbnailHeight()
     {
-        if($h = $this->getSetting('thumbnailHeight')) {
+        if ($h = $this->getSetting('thumbnailHeight')) {
             return $h;
         }
 
@@ -1456,16 +1467,16 @@ public function getConfigJSON()
     {
         $data = $this->settings;
         $defaults = $this->getDefaults();
-        foreach($this->config()->defaults as $setting => $value) {
+        foreach ($this->config()->defaults as $setting => $value) {
             $js_name = static::camelise($setting);
 
             // If the setting has been set on the instance, use that value
-            if(isset($data[$js_name])) {
+            if (isset($data[$js_name])) {
                 continue;
             }
 
             // Only include the setting in the JSON if it differs from the core default value
-            if(!isset($defaults[$js_name]) || ($defaults[$js_name] !== $value)) {
+            if (!isset($defaults[$js_name]) || ($defaults[$js_name] !== $value)) {
                 $data[$js_name] = $value;
             }
         }
@@ -1475,18 +1486,18 @@ public function getConfigJSON()
         $data['thumbnailWidth'] = $this->getSelectedThumbnailWidth();
         $data['thumbnailHeight'] = $this->getSelectedThumbnailHeight();
 
-        if(!$this->IsMultiple()) {
+        if (!$this->IsMultiple()) {
             $data['maxFiles'] = 1;
         }
 
-        if($this->isCMS()) {
+        if ($this->isCMS()) {
             $data['urlSelectDialog'] = $this->Link('select');
-            if($this->getFolderName()) {
+            if ($this->getFolderName()) {
                 $data['folderID'] = Folder::find_or_make($this->getFolderName())->ID;
             }
         }
 
-        return Convert::array2json($data);
+        return json_encode($data);
     }
 
     public function performReadonlyTransformation()
diff --git a/src/FileAttachmentFieldCleanTask.php b/src/FileAttachmentFieldCleanTask.php
index 801e450..b21e88b 100644
--- a/src/FileAttachmentFieldCleanTask.php
+++ b/src/FileAttachmentFieldCleanTask.php
@@ -4,6 +4,7 @@
 
 use SilverStripe\Dev\BuildTask;
 use SilverStripe\ORM\DB;
+
 /**
  * Delete all files being tracked that weren't saved against anything.
  *
@@ -17,7 +18,7 @@ class FileAttachmentFieldCleanTask extends BuildTask
     private static $segment = 'dropzone-clean';
 
     protected $title = "File Attachment Field - Clear all tracked files that are older than 1 hour";
-    
+
     protected $description = 'Delete files uploaded via FileAttachmentField that aren\'t attached to anything.';
 
     public function run($request)
@@ -28,10 +29,10 @@ public function run($request)
             foreach ($files as $trackRecord) {
                 $file = $trackRecord->File();
                 if ($file->exists()) {
-                    DB::alteration_message('Remove File #'.$file->ID.' from "'.$trackRecord->ControllerClass.'" on '.$trackRecord->RecordClass.' #'.$trackRecord->RecordID, 'error');
+                    DB::alteration_message('Remove File #' . $file->ID . ' from "' . $trackRecord->ControllerClass . '" on ' . $trackRecord->RecordClass . ' #' . $trackRecord->RecordID, 'error');
                     $file->delete();
                 } else {
-                    DB::alteration_message('Untrack missing File #'.$file->ID.' from "'.$trackRecord->ControllerClass.'" on '.$trackRecord->RecordClass.' #'.$trackRecord->RecordID, 'error');
+                    DB::alteration_message('Untrack missing File #' . $file->ID . ' from "' . $trackRecord->ControllerClass . '" on ' . $trackRecord->RecordClass . ' #' . $trackRecord->RecordID, 'error');
                 }
                 $trackRecord->delete();
             }
diff --git a/src/FileAttachmentFieldTrack.php b/src/FileAttachmentFieldTrack.php
index c032e9e..d80168b 100644
--- a/src/FileAttachmentFieldTrack.php
+++ b/src/FileAttachmentFieldTrack.php
@@ -49,11 +49,11 @@ public function onBeforeWrite()
                 if ($controller->hasMethod('data')) {
                     // Store page visiting on frontend (ContentController)
                     $pageRecord = $controller->data();
-                } else if ($controller->hasMethod('currentPageID')) {
+                } elseif ($controller->hasMethod('currentPageID')) {
                     // Store editing page in CMS (LeftAndMain)
                     $id = $controller->currentPageID();
                     $pageRecord = $controller->getRecord($id);
-                } else if ($controller->hasMethod('getRecord')) {
+                } elseif ($controller->hasMethod('getRecord')) {
                     $pageRecord = $controller->getRecord();
                 }
 
@@ -74,7 +74,7 @@ public function setRecord($record)
     public function Record()
     {
         if ($this->RecordClass && $this->RecordID) {
-            return DataObject::get_one($this->RecordClass, "ID = ".(int)$this->RecordID);
+            return DataObject::get_one($this->RecordClass, "ID = " . (int)$this->RecordID);
         }
     }
 }