DevTools: Deleting object property in console would just assign it to undefined.

Source/devtools/front_end/components/ObjectPropertiesSection.js

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009 Joseph Pecoraro
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 280 matching lines @@
 
     /**
      * @return {boolean}
      */
     renderPromptAsBlock: function()
     {
         return false;
     },
 
     /**
-     * @param {!Event=} event
-     * @return {!Array.<!Element|undefined>}
+     * @return {{element: !Element, value: (string|undefined)}}
      */
-    elementAndValueToEdit: function(event)
+    elementAndValueToEdit: function()
     {
-        return [this.valueElement, (typeof this.valueElement._originalTextContent === "string") ? this.valueElement._originalTextContent : undefined];
+        return {
+            element: this.valueElement,
+            value: (typeof this.valueElement._originalTextContent === "string") ? this.valueElement._originalTextContent : undefined
+        };
     },
 
     /**
      * @param {!Event=} event
      */
     startEditing: function(event)
     {
-        var elementAndValueToEdit = this.elementAndValueToEdit(event);
-        var elementToEdit = elementAndValueToEdit[0];
-        var valueToEdit = elementAndValueToEdit[1];
+        var elementAndValueToEdit = this.elementAndValueToEdit();
+        var elementToEdit = elementAndValueToEdit.element;
+        var valueToEdit = elementAndValueToEdit.value;
 
         if (WebInspector.isBeingEdited(elementToEdit) || !this.treeOutline.section.editable || this._readOnly)
             return;
 
         // Edit original source.
         if (typeof valueToEdit !== "undefined")
             elementToEdit.setTextContentTruncatedIfNeeded(valueToEdit, WebInspector.UIString("<string is too large to edit>"));
 
         var context = { expanded: this.expanded, elementToEdit: elementToEdit, previousContent: elementToEdit.textContent };
 
@@ skipping 43 matching lines @@
     },
 
     editingCommitted: function(element, userInput, previousContent, context)
     {
         if (userInput === previousContent) {
             this.editingCancelled(element, context); // nothing changed, so cancel
             return;
         }
 
         this.editingEnded(context);
-        this.applyExpression(userInput, true);
+        this.applyExpression(userInput);
     },
 
     _promptKeyDown: function(context, event)
     {
         if (isEnterKey(event)) {
             event.consume(true);
             this.editingCommitted(null, context.elementToEdit.textContent, context.previousContent, context);
             return;
         }
         if (event.keyIdentifier === "U+001B") { // Esc
             event.consume();
             this.editingCancelled(null, context);
             return;
         }
     },
 
-    applyExpression: function(expression, updateInterface)
+    /**
+     * @param {string} expression
+     */
+    applyExpression: function(expression)
     {
         expression = expression.trim();
-        var expressionLength = expression.length;
+        if (expression)
+            this.property.parentObject.setPropertyValue(this.property.name, expression, callback.bind(this));
+        else
+            this.property.parentObject.deleteProperty(this.property.name, callback.bind(this));
 
         /**
          * @param {?Protocol.Error} error
          * @this {WebInspector.ObjectPropertyTreeElement}
          */
         function callback(error)
         {
-            if (!updateInterface)
+            if (error) {
+                this.update();
                 return;
+            }
 
-            if (error)
-                this.update();
-
-            if (!expressionLength) {
+            if (!expression) {
                 // The property was deleted, so remove this tree element.
                 this.parent.removeChild(this);
             } else {
                 // Call updateSiblings since their value might be based on the value that just changed.
                 this.updateSiblings();
             }
         };
-        this.property.parentObject.setPropertyValue(this.property.name, expression.trim(), callback.bind(this));
     },
 
     /**
      * @return {string|undefined}
      */
     propertyPath: function()
     {
         if ("_cachedPropertyPath" in this)
             return this._cachedPropertyPath;
 
@@ skipping 556 matching lines @@
 {
     WebInspector.TextPrompt.call(this, WebInspector.ExecutionContextSelector.completionsForTextPromptInCurrentContext);
     this.setSuggestBoxEnabled(true);
     if (renderAsBlock)
         this.renderAsBlock();
 }
 
 WebInspector.ObjectPropertyPrompt.prototype = {
     __proto__: WebInspector.TextPrompt.prototype
 }