Output of list with empty string is the same to empty list

Entrypoint in the image is `[]`. If I create the following metadata test:
```
metadataTest:
  entrypoint: [""]
```
it will fail with error message:
```
    --- FAIL: TestAll/Metadata_Test (0.00s)
        structure.go:179: Image entrypoint [] does not match expected entrypoint: []
```