<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def to_internal_value(self, data):
 """ Updates _validated_data with dynamic data, i.e. data, not listed in fields. """

        ret = super(DynamicDocumentSerializer, self).to_internal_value(data)
        dynamic_data = self._get_dynamic_data(ret)
        ret.update(dynamic_data)
        return ret