Defend against empty variable names

core/ui/fields/field_variable.js

@@ -153,10 +153,9 @@ Blockly.FieldVariable.prototype.dropdownChange = function(text) {
         Blockly.Msg.CONFIRM_CREATE_VARIABLE,
         '',
         function(newVar) {
-          this.setText(newVar);
-          // Since variables are case-insensitive, ensure that if the new variable
-          // matches with an existing variable, the new case prevails throughout.
-          Blockly.Variables.renameVariable(newVar, newVar, this.sourceBlock_.blockSpace);
+          if (newVar) {
+            this.setText(newVar);
+          }
         }.bind(this));
     return null;
   }

core/utils/variables.js

@@ -128,7 +128,7 @@ Blockly.Variables.getVars = function (opt_category) {
  * @param {Blockly.BlockSpace} blockSpace BlockSpace to rename child blocks of
  */
 Blockly.Variables.renameVariable = function(oldName, newName, blockSpace) {
-  if (newName === oldName) {
+  if (newName === oldName || !newName) {
     return;
   }
   var blocks = blockSpace.getAllBlocks({shareMainModal: false});

tests/variables_test.js

@@ -65,3 +65,17 @@ function test_allVariablesOtherCategory() {
 
   goog.dom.removeNode(container);
 }
+
+function test_cannotRenameVariablesToEmpty() {
+  var container = Blockly.Test.initializeBlockSpaceEditor();
+
+  var blockXML = '<xml><block type="variables_get"><title name="VAR">i</title></block></xml>';
+  Blockly.Xml.domToBlockSpace(Blockly.mainBlockSpace, Blockly.Xml.textToDom(blockXML));
+
+  Blockly.Variables.renameVariable("i", "z", Blockly.mainBlockSpace);
+  assertEquals("Variable renamed to 'z'", 'z', Blockly.Variables.allVariables()[0]);
+  Blockly.Variables.renameVariable("z", "", Blockly.mainBlockSpace);
+  assertEquals("Cannot rename var to empty", 'z', Blockly.Variables.allVariables()[0]);
+
+  goog.dom.removeNode(container);
+}