2 question mark dart code example
Example 1: dart double question mark
// This means a equals b, but if b is null then a equals 'hello'.
String a = b ?? 'hello';
// This means if b is null then set it equal to hello. Otherwise, don't change it.
b ??= 'hello';
Example 2: dart double question mark
// This means a equals b, but if b is null then a equals 'hello'.
String a = b ?? 'hello';