<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def set_multivar(self, section, option, value=''):
        '''
        This function is unique to the GitConfigParser. It will add another
        value for the option if it already exists, converting the option's
        value to a list if applicable.

        If "value" is a list, then any existing values for the specified
        section and option will be replaced with the list being passed.
        '''
        self._string_check(value, allow_list=True)
        if not section or section == self.DEFAULTSECT:
            sectdict = self._defaults
        else:
            try:
                sectdict = self._sections[section]
            except KeyError:
                raise NoSectionError(  # pylint: disable=undefined-variable
                    salt.utils.stringutils.to_str(section))
        key = self.optionxform(option)
        self._add_option(sectdict, key, value)