guava/src/com/google/common/collect/ForwardingSortedMap.java
@SuppressWarnings("unchecked")
  private int unsafeCompare(Object k1, Object k2) {
    Comparator<? super K> comparator = comparator();
    if (comparator == null) {
      return ((Comparable<Object>) k1).compareTo(k2);
    } else {
      return ((Comparator<Object>) comparator).compare(k1, k2);
    }
  }
@SuppressWarnings("unchecked")
  private int unsafeCompare(Object k1, Object k2) {
    Comparator<? super K> comparator = comparator();
    if (comparator == null) {
      return ((Comparable<Object>) k1).compareTo(k2);
    } else {
      return ((Comparator<Object>) comparator).compare(k1, k2);
    }
  }
unsafe, but worst case is a CCE is thrown, which callers will be expecting