first level testing for rending v3 model in place.

Now onto some hardening tests, lets re-render each spec after reading to check for failures.

datamodel/high/base/external_doc.go

@@ -56,9 +56,6 @@ func (e *ExternalDoc) Render() ([]byte, error) {
 
 // MarshalYAML will create a ready to render YAML representation of the ExternalDoc object.
 func (e *ExternalDoc) MarshalYAML() (interface{}, error) {
-	if e == nil {
-		return nil, nil
-	}
 	nb := high.NewNodeBuilder(e, e.low)
 	return nb.Render(), nil
 }