Automatic merge from submit-queue (batch tested with PRs 47403, 46646, 46906, 46527, 46792)
Add test case for namespace
**What this PR does / why we need it**:
Unit test case need add that when name is "".
**Special notes for your reviewer**:
refer to https://github.com/kubernetes/kubernetes/blob/master/pkg/kubectl/namespace.go#L74
**Release note**:
```release-note
NONE
```