message: use an empty initializer to create map
diff: @@ -193,11 +193,9 @@ void InferShapes(
  const std::unordered_map<std::string, int>& opset_imports,
  const ISchemaRegistry* schema_registry,
  const IFunctionBuilderRegistry* func_registry) {
  - const std::unordered_map<std::string, TypeProto*>
  - outer_scope_value_types_by_name;
  InferShapesImpl(
  g,
  - outer_scope_value_types_by_name,
  + {},
  opset_imports,
  schema_registry,
  func_registry);
  @@ -213,12 +211,9 @@ void InferShapes(
  static_cast<int>(opset_import.version());
  }
  auto* g = m.mutable_graph();
  - const std::unordered_map<std::string, TypeProto*>
  - outer_scope_value_types_by_name;
  -
  InferShapesImpl(
  g,
  - outer_scope_value_types_by_name,
  + {},
  opset_imports,
  schema_registry,
  func_registry);
  