When user call the `Call()` method, they don't always want to sent some args or get the return value, so they use `nil` when call `Call()` method and this will casue an error. It's better to not trying to encode or decode if it's nil. Signed-off-by: Lei Jitang <leijitang@huawei.com> Upstream-commit: a2d348968fe754df41d0a1b56c7ba29ebbaa6849 Component: engine