indexOf method Null safety

int indexOf(
  1. E element,
  2. [int start = 0]

The first index of element in this list.

Searches the list from index start to the end of the list. The first time an object o is encountered so that o == element, the index of o is returned.

var notes = ['do', 're', 'mi', 're'];
notes.indexOf('re');    // 1
notes.indexOf('re', 2); // 3

Returns -1 if element is not found.

notes.indexOf('fa');    // -1


int indexOf(E element, [int start = 0]);