Fix for crash when part directive uri is has null value.

pkg/analyzer/test/generated/compile_time_error_code_driver_test.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'compile_time_error_code_test.dart';
 
 main() {
   defineReflectiveSuite(() {
@@ skipping 59 matching lines @@
   @override
   test_typeAliasCannotReferenceItself_typeVariableBounds() {
     return super.test_typeAliasCannotReferenceItself_typeVariableBounds();
   }
 
   @failingTest
   @override
   test_uriDoesNotExist_import_appears_after_deleting_target() {
     return super.test_uriDoesNotExist_import_appears_after_deleting_target();
   }
-
-  @failingTest
-  @override
-  test_uriWithInterpolation_nonConstant() {
-    return super.test_uriWithInterpolation_nonConstant();
-  }
 }