@Nullable
        protected T execute(@Nullable Reference<K, V> ref, @Nullable Entry<K, V> entry) {
            return null;
        }
Convenience method that can be used for tasks that do not need access to {link Entries}.

@param ref   the found reference (or {@code null})
@param entry the found entry (or {@code null})
@return the result of the task
see #execute(Reference, Entry, Entries)
analyzer/src/main/java/nl/basjes/parse/useragent/utils/springframework/util/ConcurrentReferenceHashMap.java