Fix for NPE in navigation after some incremental changes.

pkg/analysis_server/lib/src/protocol_server.dart

Index: pkg/analysis_server/lib/src/protocol_server.dart
diff --git a/pkg/analysis_server/lib/src/protocol_server.dart b/pkg/analysis_server/lib/src/protocol_server.dart
index 26caf44a99f7368d6778230746f27831abcad2a1..74d483efdfc89d764b24c507f18740968d0e46e1 100644
--- a/pkg/analysis_server/lib/src/protocol_server.dart
+++ b/pkg/analysis_server/lib/src/protocol_server.dart
@@ -230,6 +230,11 @@ NavigationTarget newNavigationTarget_fromElement(engine.Element element,
     int fileToIndex(String file)) {
   ElementKind kind = newElementKind_fromEngine(element.kind);
   Location location = newLocation_fromElement(element);
+  // TODO(scheglov) Fix the enclosing element problem in the incremental
+  // resolver and remove this.
+  if (location == null) {
+    return null;
+  }
   String file = location.file;
   int fileIndex = fileToIndex(file);
   return new NavigationTarget(