checker/tests/nullness/java8inference/InLambda.java

public class InLambda {
  static class Mine<T> {
    @SuppressWarnings("nullness") // just a utility
    static <S> Mine<S> some() {
      return null;
    }
  }

  interface Function<T, R> {
    R apply(T t);
  }

  interface Box<V> {}

  static class Boxes {
    @SuppressWarnings("nullness") // just a utility
    static <O> Box<O> transform(Function<String, ? extends O> function) {
      return null;
    }
  }

  class Infer {
    Box<Mine<Integer>> f =
        Boxes.transform(
            el -> {
              return Mine.some();
            });
  }
}