Inference: stuck expressions should not be considered ahead of target-type constraints evaluation

The following program should fail to compile but it doesn't:

import java.util.*;
import java.util.function.*;

class ObjectTargetType {

<T, R> R m(List<? extends R> l1, List<? extends R> l2, Function<String, R> fun) {
    return fun.apply(null);
}

void test(List<Class<RuntimeException>> l1, List<Class<Exception>> l2) {
    Object o = m(l1, l2, s -> String.class); // error???
}

}