code: public <K, V> SortedMap<K, V> headMap(SortedMap<K, V> map, K toKey) {
          return map.headMap(toKey);
      }
docs: Get the sorted map of all key/value pairs where the keys are less than
  the given key based on the sort algorithm of the keys in the map.
  
  @param <K> The component type of the keys
  @param <V> The component type of the values
  
  @param map The sorted map to retrieve from
  @param toKey The key, exclusive, to retrieve up to
  
  @return A new sorted map of all key/value pairs up to the given key
  
  @see SortedMap#headMap(Object)