code: public static <K, V> SortedMap<K, V> nullToEmpty(final SortedMap<K, V> map) {
          return map == null ? N.<K, V> emptySortedMap() : map;
      }
docs: Returns an immutable empty <code>SortedMap</code> if the specified SortedMap is <code>null</code>, otherwise itself is returned.
  
  @param map
  @return