code: @Pure
  	@Inline(value = "$3.union($1, $4.singletonMap($2.getKey(), $2.getValue()))",
  			imported = { MapExtensions.class, Collections.class })
  	public static <K, V> Map<K, V> operator_plus(Map<K, V> left, final Pair<? extends K, ? extends V> right) {
  		return union(left, Collections.singletonMap(right.getKey(), right.getValue()));
  	}
docs: Add the given pair to a given map for obtaining a new map.
  
  <p>
  The replied map is a view on the given map. It means that any change
  in the original map is reflected to the result of this operation.
  </p>
  
  <p>
  Even if the key of the right operand exists in the left operand, the value in the right operand is preferred.
  </p>
  
  @param <K> type of the map keys.
  @param <V> type of the map values.
  @param left the map to consider.
  @param right the entry (key, value) to add into the map.
  @return an immutable map with the content of the map and with the given entry.
  @throws IllegalArgumentException - when the right operand key exists in the left operand.
  @since 2.15