code: @Pure
  	@Inline(value = "$3.union($1, $2)", imported = MapExtensions.class)
  	public static <K, V> Map<K, V> operator_plus(Map<K, V> left, Map<? extends K, ? extends V> right) {
  		return union(left, right);
  	}
docs: Merge the two maps.
  
  <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>
  If a key exists in the left and right operands, 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 left map.
  @param right the right map.
  @return a map with the merged contents from the two maps.
  @throws IllegalArgumentException - when a right operand key exists in the left operand.
  @since 2.15