Detect undefined elements in the debugger and remove undefined elem if a row has no elements when adding spacers. (#3576)

core/renderers/common/debugger.js

@@ -282,7 +282,12 @@ Blockly.blockRendering.Debug.prototype.drawRenderedRow = function(row, cursorY,
  * @package
  */
 Blockly.blockRendering.Debug.prototype.drawRowWithElements = function(row, cursorY, isRtl) {
-  for (var i = 0, elem; (elem = row.elements[i]); i++) {
+  for (var i = 0, l = row.elements.length; i < l; i++) {
+    var elem = row.elements[i];
+    if (!elem) {
+      console.warn('A row has an undefined or null element.', row, elem);
+      continue;
+    }
     if (Blockly.blockRendering.Types.isSpacer(elem)) {
       this.drawSpacerElem(
           /** @type {!Blockly.blockRendering.InRowSpacer} */ (elem),

core/renderers/common/info.js

@@ -435,6 +435,9 @@ Blockly.blockRendering.RenderInfo.prototype.addElemSpacing_ = function() {
       row.elements.push(new Blockly.blockRendering.InRowSpacer(
           this.constants_, this.getInRowSpacing_(null, oldElems[0])));
     }
+    if (!oldElems.length) {
+      continue;
+    }
     for (var e = 0; e < oldElems.length - 1; e++) {
       row.elements.push(oldElems[e]);
       var spacing = this.getInRowSpacing_(oldElems[e], oldElems[e + 1]);

core/renderers/geras/info.js

@@ -143,6 +143,9 @@ Blockly.geras.RenderInfo.prototype.addElemSpacing_ = function() {
       row.elements.push(new Blockly.blockRendering.InRowSpacer(
           this.constants_, this.getInRowSpacing_(null, oldElems[0])));
     }
+    if (!oldElems.length) {
+      continue;
+    }
     for (var e = 0; e < oldElems.length - 1; e++) {
       row.elements.push(oldElems[e]);
       var spacing = this.getInRowSpacing_(oldElems[e], oldElems[e + 1]);