Give useful message for null derefs

sdk/lib/_internal/js_runtime/lib/core_patch.dart

Index: sdk/lib/_internal/js_runtime/lib/core_patch.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/core_patch.dart b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
index 5d84791f113a18360f42f0b0c11f2bdc1b07c59f..8e4fdef830814f1e4501af428a3fd895371aaed0 100644
--- a/sdk/lib/_internal/js_runtime/lib/core_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
@@ -65,6 +65,18 @@ class Object {
   Type get runtimeType => getRuntimeType(this);
 }
 
+// Patch for Null implementation
+@patch
+class Null {
+  @patch
+  dynamic noSuchMethod(Invocation invocation) {
+    String name = _symbolToString(invocation.memberName);
+    if (invocation.isMethod)
+      throw new NullDereferenceError('$name() was called on a null value.');
+    throw new NullDereferenceError('$name was accessed on a null value.');
+  }
+}
+
 // Patch for Function implementation.
 @patch
 class Function {