@Override
  public String toString() {
    return MoreObjects.toStringHelper(getClass().getSimpleName())
            .add("value", value())
            .add("type", returnType().getTypeName())
            .toString();

  }
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