CallApi 当 AK 为空时会导致空指针异常

```go
resp, err := client.CallApi(params, request, runtime)
```

error: 

```go
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x0 pc=0x102bc01f8]
```

猜测可能是鉴权过程中的某一步出现了 nil，希望能在鉴权时捕获非法的 AK，方便排查错误