Null coalescing operators return the right hand side of an expression of
the left hand side is null.


1. The `??` operator returns the right hand side of the expression if the
left hand side evaluates to `null`.

-- Expect stdout --
is null
false
0
-- End --

-- Testcase --
{%
	x = null;
	y = false;
	z = 0;

	print(x ?? "is null", "\n");
	print(y ?? "is null", "\n");
	print(z ?? "is null", "\n");
%}
-- End --


2. The `??=` nullish assignment operator sets the left hand side variable
or value to the right hand side expression if the existing value is null.

-- Expect stdout --
is null
false
0
-- End --

-- Testcase --
{%
	x = null;
	y = false;
	z = 0;

	x ??= "is null";
	y ??= "is null";
	z ??= "is null";

	print(x, "\n");
	print(y, "\n");
	print(z, "\n");
%}
-- End --