Gracefully degrade if no source for completion

pkg/analysis_server/lib/src/domain_completion.dart

Index: pkg/analysis_server/lib/src/domain_completion.dart
diff --git a/pkg/analysis_server/lib/src/domain_completion.dart b/pkg/analysis_server/lib/src/domain_completion.dart
index affe17c46e87a27371072af69648e3c5025594a1..676b0f54e1a67927e2775b0357714cb23580f2ad 100644
--- a/pkg/analysis_server/lib/src/domain_completion.dart
+++ b/pkg/analysis_server/lib/src/domain_completion.dart
@@ -177,6 +177,9 @@ class CompletionDomainHandler implements RequestHandler {
     ContextSourcePair contextSource = server.getContextSourcePair(params.file);
     AnalysisContext context = contextSource.context;
     Source source = contextSource.source;
+    if (!context.exists(source)) {

[scheglov, 2015/03/30 21:10:48]

Actually it is not guaranteed that AnalysisContext is not null.
It might be if the file is not a part of any context.

[danrubel, 2015/03/30 21:40:48]

Good catch. Fixed.

+      return new Response.unknownSource(request);
+    }
     recordRequest(performance, context, source, params.offset);
     if (manager == null) {
       manager = completionManagerFor(context, source);