Analyzer: Don't allow extending or implementing Null.

editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/internal/resolver/TestTypeProvider.java

Index: editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/internal/resolver/TestTypeProvider.java
diff --git a/editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/internal/resolver/TestTypeProvider.java b/editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/internal/resolver/TestTypeProvider.java
index cf0957dbd2e9d6543c2b487034a574a12d521f8a..e4e79ad067558719724d87fec691478a4ac65a49 100644
--- a/editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/internal/resolver/TestTypeProvider.java
+++ b/editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/internal/resolver/TestTypeProvider.java
@@ -1,11 +1,11 @@
 /*
  * Copyright (c) 2013, the Dart project authors.
- * 
+ *
  * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
- * 
+ *
  * http://www.eclipse.org/legal/epl-v10.html
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software distributed under the License
  * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
  * or implied. See the License for the specific language governing permissions and limitations under
@@ -89,6 +89,11 @@ public class TestTypeProvider implements TypeProvider {
   private InterfaceType mapType;
 
   /**
+   * The type representing the built-in type 'Null'.
+   */
+  private InterfaceType nullType;
+
+  /**
    * The type representing the built-in type 'num'.
    */
   private InterfaceType numType;
@@ -236,6 +241,14 @@ public class TestTypeProvider implements TypeProvider {
   }
 
   @Override
+  public InterfaceType getNullType() {
+    if (nullType == null) {
+      nullType = classElement("Null").getType();
+    }
+    return nullType;
+  }
+
+  @Override
   public InterfaceType getNumType() {
     if (numType == null) {
       initializeNumericTypes();
@@ -387,7 +400,7 @@ public class TestTypeProvider implements TypeProvider {
   /**
    * Given a class element representing a class with type parameters, propagate those type
    * parameters to all of the accessors, methods and constructors defined for the class.
-   * 
+   *
    * @param classElement the element representing the class with type parameters
    */
   private void propagateTypeArguments(ClassElementImpl classElement) {