Entry<K, V> entryToRemove = entrySet.iterator().next();
    Set<Entry<K, V>> entriesToRemove = singleton(entryToRemove);
    if (supportsRemove) {
      // We use a copy of "entryToRemove" in the assertion because "entryToRemove" might be
      // invalidated and have undefined behavior after entrySet.removeAll(entriesToRemove),
      // for example entryToRemove.getValue() might be null.