Fetch one row, just like DB-API cursor.fetchone().

After all rows have been exhausted, the underlying DBAPI cursor resource is released, and the object may be safely discarded.

Calls to _engine.ResultProxy.fetchone() after all rows have been exhausted will return None. After the _engine.ResultProxy.close() method is called, the method will raise ResourceClosedError.

Returns:a RowProxy object, or None if no rows remain