Provider API returns 500 with GPU must not be nil

[stalniy]

Describe the bug
This error is caught by console observability stack.

Every time provider API responds with 500, console assumes it's a server error on provider and proxies back 503 to the user. Obviously, user will retry such request without understanding the underlying issue. This is misleading for both console provider proxy and for the end user. So, user doesn't understand why he can't use that provider

To Reproduce
Don't know the exact SDL, but somehow gpu is null

Expected behavior
Provider proxy should return 4xx errors on client error

Additional context

This happens on manifest send: https://provider.europlots.com:8443/deployment/25382596/manifest