@environmentfilter
def do_first(environment, seq):
    try:
        return next(iter(seq))
    except StopIteration:
        return environment.undefined('No first item, sequence was empty.')
Check that `radio_fields` is a dictionary.
dataset/ETHPy150Open GoogleCloudPlatform/appengine-flask-skeleton/lib/jinja2/filters.py/do_first--crossover with--dataset/ETHPy150Open django/django/django/contrib/admin/checks.py/BaseModelAdminChecks._check_radio_fields