def optgroups(self, name, value, attrs=None):
if not self.is_required and not self.allow_multiple_selected:<EOL><INDENT>self.choices = list(chain([('<STR_LIT>', '<STR_LIT>')], self.choices))<EOL><DEDENT>return super(Select2Mixin, self).optgroups(name, value, attrs=attrs)<EOL>
Add empty option for clearable selects.