checker/tests/nullness/Issue3792.java

import java.util.Collection;
import java.util.NavigableMap;

public abstract class Issue3792<T> {
  static class Instant {}

  void method(
      NavigableMap<Instant, Collection<T>> contents, Instant minTimestamp, Instant limitTimestamp) {
    contents.subMap(minTimestamp, true, limitTimestamp, false).entrySet().stream()
        .flatMap(e -> e.getValue().stream().map(v -> of(v, e.getKey())));
  }

  abstract Object of(T v, Instant key);
}