Fix for NPE if subscribing for errors in a not analyzed file.

pkg/analysis_server/test/domain_analysis_test.dart

Index: pkg/analysis_server/test/domain_analysis_test.dart
diff --git a/pkg/analysis_server/test/domain_analysis_test.dart b/pkg/analysis_server/test/domain_analysis_test.dart
index f9ee43c93f31b64520b751b0bda2f16fae9ab959..b4b0442e015fee7e3f985198c2766d61c3380bf6 100644
--- a/pkg/analysis_server/test/domain_analysis_test.dart
+++ b/pkg/analysis_server/test/domain_analysis_test.dart
@@ -325,6 +325,19 @@ void test_setSubscriptions() {
       });
     });
   });
+
+  test('after analysis, no such file', () {
+    AnalysisTestHelper helper = new AnalysisTestHelper();
+    helper.createSingleFileProject('int V = 42;');
+    return helper.waitForOperationsFinished().then((_) {
+      String noFile = '/no-such.file.dart';
+      helper.addAnalysisSubscriptionErrors(noFile);
+      return helper.waitForOperationsFinished().then((_) {
+        var errors = helper.getErrors(noFile);
+        expect(errors, isEmpty);
+      });
+    });
+  });
 }
 
 
@@ -484,6 +497,10 @@ class AnalysisTestHelper {
     handleSuccessfulRequest(request);
   }
 
+  void addAnalysisSubscriptionErrors(String file) {
+    addAnalysisSubscription(AnalysisService.ERRORS, file);
+  }
+
   void addAnalysisSubscriptionHighlights(String file) {
     addAnalysisSubscription(AnalysisService.HIGHLIGHTS, file);
   }