fix: ensure timeout not nil to avoid attempt to perform arithmetic on a nil value error

[nic-chen]

error logs:

The cause of the issue is that in the function refresh_jwt_token, the parameter timeout of semaphore wait directly uses the parameter passed by the caller without considering that the timeout parameter may be nil. If the caller does not pass the parameter timeout, this error will be triggered:

The timeout passed to the function refresh_jwt_token is basically self.timeout:

Since the timeout passed to the function refresh_jwt_token is basically self.timeout, we make a judgment on the timeout parameter in refresh_jwt_token, If it is nil, just use self.timeout, if self.timeout is nil too, just use 0, to ensure the timeout is not nil to avoid the error.