/**
   * Ensures that this type token doesn't contain type variables, which can cause unchecked type
   * errors for callers like {@link TypeToInstanceMap}.
   */
  @CanIgnoreReturnValue
  final TypeToken<T> rejectTypeVariables() {
    new TypeVisitor() {
      @Override
      void visitTypeVariable(TypeVariable<?> type) {
        throw new IllegalArgumentException(