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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _populate_validated_data_with_sub_field_data(self, validated_data):
 """ Move field data nested in `ModelSubSerializer` fields back into the overall validated data dict. """

        for fieldname, field in self.get_fields().items():
            if isinstance(field, ModelSubSerializer):
                field_data = validated_data.pop(fieldname, None)
                if field_data:
                    validated_data.update(field_data)