Django: CharField that will save an empty string as NULL

char_field_no_empty_string.py

class CharFieldNoEmptyString(CharField):
    def get_prep_value(self, value):
        # Cast empty strings to null before saving to the DB.
        value = (
            super(CharFieldNoEmptyString, self)
            .get_prep_value(value)
        )
        return value or None