guava/src/com/google/common/util/concurrent/AtomicLongMap.java
@CanIgnoreReturnValue
  public long remove(K key) {
    Long result = map.remove(key);
    return (result == null) ? 0L : result.longValue();
  }
@CanIgnoreReturnValue
  public long remove(K key) {
    Long result = map.remove(key);
    return (result == null) ? 0L : result.longValue();
  }
Removes and returns the value associated with {@code key}. If {@code key} is not in the map,
this method has no effect and returns zero.