message: Skip null nodes in the Kythe extractor code
diff: @@ -743,6 +743,7 @@ void IndexingFactsTreeExtractor::ExtractModulePort(
  if (tag == NodeEnum::kPortDeclaration) {
  const SyntaxTreeLeaf* leaf =
  GetIdentifierFromModulePortDeclaration(module_port_node);
  + if (!leaf) return;
  facts_tree_context_.top().NewChild(IndexingNodeData(
  IndexingFactType::kVariableDefinition, Anchor(leaf->get())));
  @@ -751,6 +752,7 @@ void IndexingFactsTreeExtractor::ExtractModulePort(
  // module m(a, b);
  const SyntaxTreeLeaf* leaf =
  GetIdentifierFromPortReference(module_port_node);
  + if (!leaf) return;
  if (has_propagated_type) {
  // Check if the last type was not a primitive type.
  @@ -835,9 +837,11 @@ void IndexingFactsTreeExtractor::ExtractInputOutputDeclaration(
  GetSymbolIdentifierFromIdentifierUnpackedDimensions(
  identifier_unpacked_dimension);
  + if (port_name_leaf) {
  facts_tree_context_.top().NewChild(IndexingNodeData(
  IndexingFactType::kVariableDefinition, Anchor(port_name_leaf->get())));
  }
  +}
  void IndexingFactsTreeExtractor::ExtractModuleOrInterfaceOrProgramEnd(
  const SyntaxTreeNode& module_declaration_node) {
  @@ -1140,6 +1144,7 @@ void IndexingFactsTreeExtractor::ExtractFunctionOrTaskOrConstructorPort(
  // port variable name.
  const SyntaxTreeLeaf* port_identifier =
  GetIdentifierFromTaskFunctionPortItem(*port.match);
  + if (!port_identifier) continue;
  // variable identifier node.
  IndexingFactNode variable_node(
  @@ -1271,7 +1276,9 @@ void IndexingFactsTreeExtractor::ExtractMethodCallExtension(
  {
  const SyntaxTreeLeaf* fun_call =
  GetFunctionCallNameFromCallExtension(call_extension_node);
  - if (fun_call) function_node.Value().AppendAnchor(Anchor(fun_call->get()));
  + if (fun_call) {
  + function_node.Value().AppendAnchor(Anchor(fun_call->get()));
  + }
  }
  {
  @@ -1299,9 +1306,10 @@ void IndexingFactsTreeExtractor::ExtractMemberExtension(
  const verible::SyntaxTreeLeaf* unqualified =
  GetUnqualifiedIdFromHierarchyExtension(hierarchy_extension_node);
  // member name
  - if (unqualified)
  + if (unqualified) {
  member_node.Value().AppendAnchor(Anchor(unqualified->get()));
  }
  + }
  facts_tree_context_.top().NewChild(std::move(member_node));
  }
  @@ -1315,8 +1323,9 @@ void IndexingFactsTreeExtractor::ExtractClassDeclaration(
  &class_node);
  // Extract class name.
  const SyntaxTreeLeaf* class_name = GetClassName(class_declaration);
  - if (class_name)
  + if (class_name) {
  facts_tree_context_.top().Value().AppendAnchor(Anchor(class_name->get()));
  + }
  // Extract class name after endclass.
  const SyntaxTreeLeaf* class_end_name = GetClassEndLabel(class_declaration);
  @@ -1746,6 +1755,7 @@ void IndexingFactsTreeExtractor::ExtractEnumTypeDeclaration(
  // Extract enum type name.
  const SyntaxTreeLeaf* enum_type_name =
  GetIdentifierFromTypeDeclaration(enum_type_declaration);
  + if (!enum_type_name) return;
  facts_tree_context_.top().NewChild(IndexingNodeData(
  IndexingFactType::kVariableDefinition, Anchor(enum_type_name->get())));
  @@ -1831,6 +1841,7 @@ void IndexingFactsTreeExtractor::ExtractDataTypeImplicitIdDimensions(
  std::pair<const SyntaxTreeLeaf*, int> variable_name =
  GetSymbolIdentifierFromDataTypeImplicitIdDimensions(
  data_type_implicit_id_dimensions);
  + if (!variable_name.first) return;
  IndexingFactNode variable_node(
  IndexingNodeData(IndexingFactType::kVariableDefinition,
  