Fix an npe in context_manager.dart.

pkg/analysis_server/lib/src/context_manager.dart

Index: pkg/analysis_server/lib/src/context_manager.dart
diff --git a/pkg/analysis_server/lib/src/context_manager.dart b/pkg/analysis_server/lib/src/context_manager.dart
index 03c593699047a48d7d901fc68be86aed5900beff..e7460a9412159c7d8cf6055fa964ce14e23ceaa6 100644
--- a/pkg/analysis_server/lib/src/context_manager.dart
+++ b/pkg/analysis_server/lib/src/context_manager.dart
@@ -1044,7 +1044,7 @@ class ContextManagerImpl implements ContextManager {
       ContextBuilder builder =
           callbacks.createContextBuilder(info.folder, defaultContextOptions);
       AnalysisOptions options = builder.getAnalysisOptions(contextRoot,
-          contextRoot: info.analysisDriver.contextRoot);
+          contextRoot: info?.analysisDriver?.contextRoot);

[Brian Wilkerson, 2017/05/30 21:39:47]

It would be good to understand why the info is null, because I wouldn't have
expected it to be null at this point. (For example, a quick look indicates that
we might have a path that isn't being analyzed, in which case we probably should
catch it earlier.)

       SourceFactory factory = builder.createSourceFactory(contextRoot, options);
       if (enableNewAnalysisDriver) {
         AnalysisDriver driver = info.analysisDriver;