def get_documents(self, sql_string, database_name=None, collection_name=None, partition_key=None):
        """
        Get a list of documents from an existing collection in the CosmosDB database via SQL query.
        """
        if sql_string is None:
            raise AirflowBadRequest("SQL query string cannot be None")

        # Query them in SQL
        query = {'query': sql_string}

        try:
            result_iterable = self.get_conn().QueryItems(
                get_collection_link(
                    self.__get_database_name(database_name),
                    self.__get_collection_name(collection_name)),
                query,
                partition_key)

            return list(result_iterable)
        except HTTPFailure:
            return None
Get a list of documents from an existing collection in the CosmosDB database via SQL query.