    def get(self, user_name=None, server_name=''):
        """GET renders form for spawning with user-specified options

        or triggers spawn via redirect if there is no form.
        """
        # two-stage to get the right signature for @require_scopes filter on user_name
        if user_name is None:
            user_name = self.current_user.name
        if server_name is None:
            server_name = ""
        return self._get(user_name=user_name, server_name=server_name)
GET renders form for spawning with user-specified options

or triggers spawn via redirect if there is no form.
jupyterhub/handlers/pages.py