<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _new_meta_column(self, name):
 """Add a column to meta if it doesn't exist, set to value `np.nan`"""

        if name is None:
            raise ValueError('cannot add a meta column `{}`'.format(name))
        if name not in self.meta:
            self.meta[name] = np.nan