Merge pull request #5153 from Polymer/null-template-inheritance

Returning null in template should nullify parent template

lib/mixins/element-mixin.html

@@ -311,9 +311,9 @@
           } else {
             template = template.cloneNode(true);
           }
-          this.prototype._template = template;
         }
 
+        this.prototype._template = template;
       }
 
       /**

test/unit/inheritance.html

@@ -113,6 +113,24 @@
     </script>
   </dom-module>
 
+  <dom-module id="parent-element-template-overriding">
+    <script>
+    HTMLImports.whenReady(function() {
+      class ParentElementWithTemplate extends Polymer.Element {
+        static get template() {
+          return Polymer.html`This template should not exist`;
+        }
+      }
+      class ChildWithNoTemplate extends ParentElementWithTemplate {
+        static get template() {
+          return null;
+        }
+      }
+      customElements.define('child-with-no-template', ChildWithNoTemplate);
+    });
+    </script>
+  </dom-module>
+
   <test-fixture id="basic">
     <template>
       <base-el></base-el>
@@ -237,6 +255,23 @@
       assert.equal(child.handleCustomEvent.callCount, 1);
     });
   });
+
+  suite('child overriding a template', function() {
+    let el;
+
+    setup(function() {
+      el = document.createElement('child-with-no-template');
+      document.body.appendChild(el);
+    });
+
+    teardown(function() {
+      document.body.removeChild(el);
+    });
+
+    test('returning null nullifies the parent template', function() {
+      assert.equal(el.shadowRoot, null);
+    });
+  });
   </script>
 </body>
-</html>
+</html>