def get_unit_by_index(self, unit_index) -> typing.Optional['<STR_LIT>']:
if unit_index in self._section_group['<STR_LIT>'].keys():<EOL><INDENT>if unit_index not in self.__units.keys():<EOL><INDENT>_category = self.units_class_enum[self.group_category]  <EOL>self.__units[unit_index] = _category(self.d, self.l10n, self.coa_color,<EOL>self.country_index,<EOL>self.group_category,<EOL>self.group_index, unit_index)<EOL><DEDENT>return self.__units[unit_index]<EOL><DEDENT>return None<EOL>
Args:
    unit_index: index of unit

Returns: a unit of this group