[LuisFigueroaG]

References to other Issues or PRs

No issue. Same kind of bug as #7552, but for the query string: FieldMaskFromRequestBody no longer adds an empty path for {}, while ?update_mask= still does.

Have you read the Contributing Guidelines?

Yes

Brief description of what is fixed or changed

A google.protobuf.FieldMask query parameter is parsed with strings.Split(value, ","), and strings.Split("", ",") returns [""]. So an empty value produces a mask with one empty path:

msg := &examplepb.Proto3Message{}
_ = runtime.PopulateQueryParameters(msg, url.Values{"fieldmask_value": {""}}, utilities.NewDoubleArray(nil))
// msg.FieldmaskValue.Paths == []string{""}

A PATCH with ?update_mask= therefore reaches the backend with update_mask: {paths: [""]}, and a server that validates the mask (e.g. fieldmaskpb.IsValid) rejects it.

With this change an empty value gives an empty mask (the field is still set, just with no paths). That matches protojson, which decodes "" into an empty FieldMask. Non-empty values are parsed as before.

Other comments

Added TestPopulateParametersFieldMask. The empty value cases fail on main.

[johanbrandhorst]

Thanks!