static Constant of(Object value) {
    if (value == null) {
      throw new NullPointerException(String.format("value is null. Use %s.ofType(Object, Class<?>)", Constant.class.getSimpleName()));
    }
    return ofType(value, value.getClass());
  }
Converts current value to collection (if it is not already). If value
is iterable returns that collection (which is most likely ImmutableList already).

@return singleton list with current value or immutable list of values depending on type
of current value.
criteria/common/src/org/immutables/criteria/expression/Constant.java