fix: Response.protocolVersion may cause NPE

[etff]

Found and fixed an issue where Response.protocolVersion may have caused NullPointerExceptions. #2314

I believe Response builder already defaults to ProtocolVersion.HTTP_1_1
and using it when the protocolVersion argument is null.

I have other ideas:

• Create another enum value UNKNOWN based on Logger.java and use it when protocolVersion argument is null.
• Leave the current code as is and handle the NullPointerException when Response is used.

If you encounter any difficulties with this change, I'd appreciate some guidance or direction.