Suppress warning for unchecked cast

src/main/java/net/kemitix/mon/maybe/Nothing.java

@@ -39,6 +39,7 @@ final class Nothing<T> implements Maybe<T> {
     static final Maybe<?> INSTANCE = new Nothing<>();
 
     @Override
+    @SuppressWarnings("unchecked")
     public <R> Maybe<R> map(final Function<T, R> f) {
         return (Maybe<R>) INSTANCE;
     }