'Return whether `records[0]` has a regular value for ``field`` in cache.'

def __contains__(self, field):

    if isinstance(field, basestring):
        field = self._recs._fields[field]
    dummy = SpecialValue(None)
    value = self._recs.env.cache[field].get(self._recs.id, dummy)
    return (not isinstance(value, SpecialValue))
