<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_metadata(self, key) -> str: """ Get the value of a metadata. Returns None if metadata does not exist. Args: key (str):
 name of the metadata Returns: str: the value of the metadata (or None) """

        return self.metadata[key] if key in self.metadata else None