code: public static <K, V> Map<K, V> leftShift(Map<K, V> self, Map.Entry<K, V> entry) {
          self.put(entry.getKey(), entry.getValue());
          return self;
      }
docs: Overloads the left shift operator to provide an easy way to append
  Map.Entry values to a Map.
  
  @param self  a Map
  @param entry a Map.Entry to be added to the Map.
  @return same map, after the value has been added to it.
  @since 1.6.0