# ifPresent method

void ifPresent([

1. void action(
   1. T
   )?

])

If a value is present, performs the given action with the value, otherwise does nothing.

`action` the action to be performed, if a value is present

Throws InvalidArgumentException if value is present and the given action is null.

## Example

    Optional<String> name = Optional.of("Eve");
    Optional<String> empty = Optional.empty();

    name.ifPresent((value) => print("Hello, $value!")); // Hello, Eve!
    empty.ifPresent((value) => print("This won't print"));

    // Useful for side effects
    Optional<List<String>> items = Optional.of(["a", "b", "c"]);
    items.ifPresent((list) => list.add("d"));

## Implementation

    void ifPresent([void Function(T)? action]) {
      if (action == null) {
        throw InvalidArgumentException('action cannot be null');
      }
      if (_value != null) {
        action(_value as T);
      }
    }