android/guava/src/com/google/common/collect/ForwardingNavigableMap.java
protected Entry<K, V> standardCeilingEntry(K key) {
    return tailMap(key, true).firstEntry();
  }
protected Entry<K, V> standardCeilingEntry(K key) {
    return tailMap(key, true).firstEntry();
  }
A sensible definition of {@link #ceilingEntry} in terms of the {@code firstEntry()} of {@link
#tailMap(Object, boolean)}. If you override {@code tailMap}, you may wish to override {@code
ceilingEntry} to forward to this implementation.