client-go/rest: check if url is nil to prevent nil pointer dereference
client-go/rest: check if url is nil to prevent nil pointer dereference

Signed-off-by: André Martins <aanm90@gmail.com>

Kubernetes-commit: 94e7b2b8fdb4028b8b9d10ce57b9b33df146beb7

kubernetes/client-go