<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def combine_data(self, command2):
 """Combines the data for this command with another."""

        if command2 is None:
            return
        self._data = self._merge(command2._data, self._data)