def add(self, item):
check_not_none(item, "<STR_LIT>")<EOL>element_data = self._to_data(item)<EOL>return self._encode_invoke(set_add_codec, value=element_data)<EOL>
Adds the specified item if it is not exists in this set.

:param item: (object), the specified item to be added.
:return: (bool), ``true`` if this set is changed after call, ``false`` otherwise.