code: @NotNull
      public static OptionalBoolean ofNullable(@Nullable Boolean value) {
          return value == null ? EMPTY : of(value);
      }
docs: Returns an {@code OptionalBoolean} with the specified value, or empty {@code OptionalBoolean} if value is null.
  
  @param value  the value which can be null
  @return an {@code OptionalBoolean}
  @since 1.2.1