framework/tests/all-systems/Issue2370.java

import java.util.Collection;
import java.util.Optional;
import java.util.stream.Stream;

@SuppressWarnings("all")
public class Issue2370 {
  private Stream<Action2370> getAction2370s(final State2370 state) {
    return Stream.of(
            toStream(state.getOnExit()).flatMap(t -> t.getAction2370s().stream()),
            toStream(state.getOnSignal()).flatMap(t -> t.getAction2370s().stream()),
            toStream(state.getOnEnter()).flatMap(t -> t.getAction2370s().stream()))
        .flatMap(actionStream -> actionStream);
  }

  private <T> Stream<T> toStream(final Collection<T> obj) {
    return Optional.ofNullable(obj)
        .map(Stream::of)
        .orElseGet(Stream::empty)
        .flatMap(Collection::stream);
  }
}

interface Action2370 {
  public Collection<Action2370> getAction2370s();
}

interface State2370 {
  public Collection<Action2370> getOnExit();

  public Collection<Action2370> getOnSignal();

  public Collection<Action2370> getOnEnter();
}