message: Handle null scopes gracefully in ReferenceExtendsInheritance().
  This is a stop-gap as these null scopes were encountered in the
  field, further analysis is needed.
  Issues
diff: @@ -1058,6 +1058,18 @@ void KytheFactsExtractor::ReferenceExtendsInheritance(
  return;
  }
  + // TODO(hzeller): should this have been detected before ?
  + // NULL vname is not encountered, but NULL scope. Issue #1128
  + if (!definitions.back().first) {
  + LOG(ERROR) << "ReferenceExtendsInheritance: NULL vname";
  + return;
  + }
  + if (!definitions.back().second) {
  + LOG(ERROR) << "ReferenceExtendsInheritance: NULL scope for vname "
  + << *definitions.back().first;
  + return;
  + }
  +
  // Create kythe facts for extends.
  const VName& derived_class_vname = vnames_context_.top();
  CreateEdge(derived_class_vname, kEdgeExtends, *definitions.back().first);
  