How to extract String from GenericRecorcd as null instead of null string?

[Check Peck]

I am working with Avro and in my avro schema I have one field like this:

     {
        "name" : "userId",
        "type" : [ "null", "string" ],
        "doc" : "some doc"
      },

This is how I am extracting userId field from GenericRecord:

    GenericRecord payload = decoder.decode(record.value());
    String userid = String.valueOf(payload.get("userId"));
    // sometimes userid comes as null string meaning like this "null"
    System.out.println(Strings.isNullOrEmpty(userid));

And because of that "null" string, my sysout prints out as false.  Is there
any way to extract userid as null instead of "null" String?

Bcoz when I check for null string it fails and if I have to accommodate
this fix, I have to add extra check with ".equals" which I want to avoid if
possible? Is there any way?