BottomNavigationBarItem({@required Widget icon, @required Widget title, Color backgroundColor })

Creates an item that is used with BottomNavigationBar.items.

The arguments icon and title should not be null.

Source 

BottomNavigationBarItem({
  @required this.icon,
  @required this.title,
  this.backgroundColor
}) {
  assert(this.icon != null);
  assert(this.title != null);
}