docs: def init_app(self, app, config=None, statsd=None):
          """Init Flask Extension."""
          if config is not None:
              self.config = config
          elif self.config is None:
              self.config = app.config
  
          self.messages = self.config.get('EXCEPTION_MESSAGE', True)
          self.prefix = self.config.get('EXCEPTION_PREFIX', DEFAULT_PREFIX)
          self.statsd = statsd