Simplify extensions merge in mergeOpenapiSchemas

[Juneezee]

From the Go specification ¹:

"3. If the map is nil, the number of iterations is 0."

Therefore, we don't need the nil checks for merging the Extensions. Just like how we did for Properties:

oapi-codegen/pkg/codegen/merge_schemas.go

Lines 202 to 210 in 66f9bb8

	// We merge all properties
	result.Properties = make(map[string]*openapi3.SchemaRef)
	for k, v := range s1.Properties {
	result.Properties[k] = v
	}
	for k, v := range s2.Properties {
	// TODO: detect conflicts
	result.Properties[k] = v
	}

Footnotes

1. https://go.dev/ref/spec#For_range ↩

[jamietanna]

Thanks @Juneezee! Would you mind merging the latest changes into your branch, also so CI can pick it up? I'm not sure I'll be able to as you're on your master branch.

More info

[Juneezee]

@jamietanna I just rebased the latest changes. Please take a look again. Thanks 😃 !

[jamietanna]

OK, so it looks like we don't have as good unit test coverage of this as I'd hoped - if I delete this whole block of code, nothing seems to change in generated code, nor do tests fail 😅

I'm happy saying that yes, from review of the changes, this looks good - but in the future (#1617) we should improve this