code: def makeHandler(self, dialect):
          
          if dialect not in self.dialects:
              m = "The dialect specified, '{}', wasn't whitelisted in change_hook".format(dialect)
              log.msg(m)
              log.msg(
                  "Note: if dialect is 'base' then it's possible your URL is malformed and we didn't regex it properly")
              raise ValueError(m)
  
          if dialect not in self._dialect_handlers:
              if dialect not in self._plugins:
                  m = "The dialect specified, '{}', is not registered as a buildbot.webhook plugin".format(dialect)
                  log.msg(m)
                  raise ValueError(m)
              options = self.dialects[dialect]
              if isinstance(options, dict) and 'custom_class' in options:
                  klass = options['custom_class']
              else:
                  klass = self._plugins.get(dialect)
              self._dialect_handlers[dialect] = klass(self.master, self.dialects[dialect])
  
          return self._dialect_handlers[dialect]
docs: create and cache the handler object for this dialect