def initial_value(self, field_name: str = None):
        """
        Get initial value of field when model was instantiated.
        """
        if self._meta.get_field(field_name).get_internal_type() == 'ForeignKey':
            if not field_name.endswith('_id'):
                field_name = field_name+'_id'

        attribute = self._diff_with_initial.get(field_name, None)

        if not attribute:
            return None

        return attribute[0]
Get initial value of field when model was instantiated.