This is an example of how a Bytebuddy agent can be used to proxy input object classes, so that it keeps track of fields being explicitly set.

In the InputProxyApplication main method a Bytebuddy agent is registered that does the following to the SearchInput class:

1. Make it implement the FieldSetTracker interface which has a public boolean isSet(String field) method.
2. Add a field fieldsSet of type HashMap.
3. Add a public boolean isSet(String field) method that checks the fieldsSet map. This is the implementation of the FieldSetTracker interface.
4. Proxy all set* methods, so that it tracks fields being set in the fieldsSet map.

In a data fetcher you can cast an input object to the FieldSetTracker interface, and check if a field was explicitly set.

@DgsQuery
public String search(SearchInput searchInput) {

    var titleIsSet = ((FieldSetTracker) searchInput).isSet("title");
    var scoreIsSet = ((FieldSetTracker) searchInput).isSet("score");

    return "Title is set "  + titleIsSet + " and score is set " + scoreIsSet;
}

On the latest JDK builds you need to run with -XX:+EnableDynamicAgentLoading to allow dynamic agent loading.