Check for a successful response code appears to be more strict than the specification

[MikeRalphson]

https://github.com/tavis-software/Tavis.OpenApi/blob/9fe10be005827f408a963976b17bf46e2351be71/src/OpenApi/Model/PathItem.cs#L23-L29

From the spec.:

The Responses Object MUST contain at least one response code, and it SHOULD be the response for a successful operation call.

This doesn't seem to allow for the default response potentially covering the successful case, and the API MAY choose to ignore the SHOULD advice anyway.