Spawned Emacs fails to load when using Emacs master

M-x esup opens up a emacs but it fails to load as

```
Obsolete name argument nil passed to esup-result constructor [226 times]
vc-call-backend: Wrong type argument: characterp, "-"
Obsolete name argument nil passed to esup-result constructor [263 times]
```

on Emacs master. What am I missing?

