value.py

    def resolve_field_value(self, issue, field_name):
        field_value = getattr(issue.fields, field_name)

        if field_value is None:
            return None

        value = getattr(field_value, 'value', field_value)

        if isinstance(value, (list, tuple)):
            if len(value) == 0:
                value = None
            else:
                values = [getattr(v, 'name', v) for v in value]
                if field_name not in self.settings['konwn_values']:
                    value = values[0]
                else:
                    try:
                        value = next(itertools.ifilter(lambda v: v in values, self.settings['known_values'][field_name]))
                    except StopIteration:
                        value = None

        return value