What are Null-aware operators?

• Dart offers some handy operators for dealing with values that might be null.
• One is the ??= assignment operator, which assigns a value to a variable only if that variable is currently null:

	int a; // The initial value of a is null.
	a ??= 3;
	print(a); // <-- Prints 3.

	a ??= 5;
	print(a); // <-- Still prints 3.

• Another null-aware operator is ??, which returns the expression on its left unless that expression’s value is null, in which case it evaluates and returns the expression on its right:

	print(1 ?? 3); // <-- Prints 1.
	print(null ?? 12); // <-- Prints 12.