<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def update_info(self, custom=None):
 """Updates the figure's suptitle. Calls self.info_string() unless custom is provided. Args: custom: Overwrite it with this string, unless None. """

        self.figure.suptitle(self.info_string() if custom is None else custom)