code: @Inline(value = "$1.put($2.getKey(), $2.getValue())", statementExpression = true)
  	public static <K, V> V operator_add(Map<K, V> map, Pair<? extends K, ? extends V> entry) {
  		return map.put(entry.getKey(), entry.getValue());
  	}
docs: Add the given pair into the map.
  
  <p>
  If the pair key already exists in the map, its value is replaced
  by the value in the pair, and the old value in the map is returned.
  </p>
  
  @param <K> type of the map keys.
  @param <V> type of the map values.
  @param map the map to update.
  @param entry the entry (key, value) to add into the map.
  @return the value previously associated to the key, or <code>null</code>
  if the key was not present in the map before the addition.
  @since 2.15