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

[MikeRalphson]

Tavis.OpenApi/src/OpenApi/Model/PathItem.cs

Lines 23 to 29 in 9fe10be

	public void AddOperation(OperationType operationType, Operation operation)
	{
	var successResponse = operation.Responses.Keys.Where(k => k.StartsWith("2")).Any();
	if (!successResponse)
	{
	throw new DomainParseException("An operation requires a successful response");
	}

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.