code: public static <T extends Enum> @Nullable T getEnum(@NotNull ServletRequest request, @NotNull String param, @NotNull Class<T> enumClass) {
      return getEnum(request, param, enumClass, null);
    }
docs: Returns a request parameter as enum value.
  @param <T> Enum type
  @param request Request.
  @param param Parameter name.
  @param enumClass Enum class
  @return Parameter value or null if it is not set or an invalid enum value.