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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 set(self, document_data, merge=False):
 """Replace the current document in the Firestore database. A write ``option`` can be specified to indicate preconditions of the "set" operation. If no ``option`` is specified and this document doesn't exist yet, this method will create it. Overwrites all content for the document with the fields in ``document_data``. This method performs almost the same functionality as :meth:`create`. The only difference is that this method doesn't make any requirements on the existence of the document (unless ``option`` is used), whereas as :meth:`create` will fail if the document already exists. Args: document_data (dict):
 Property names and values to use for replacing a document. merge (Optional[bool] or Optional[List<apispec>]):
 If True, apply merging instead of overwriting the state of the document. Returns: google.cloud.firestore_v1beta1.types.WriteResult: The write result corresponding to the committed document. A write result contains an ``update_time`` field. """

        batch = self._client.batch()
        batch.set(self, document_data, merge=merge)
        write_results = batch.commit()
        return _first_write_result(write_results)