Check if PHP function returns null or nothing

With PHP7’s return type declaration feature:

function a(): void {
    return null; // :(
}

function b(): void {
    // :)
}

function c(): void {
    return; // :)
}

If the function doesn't return anything, then you should not test it's return value. You should know which functions are expected to return something or nothing at all - even if you're not the one who wrote them.

It's not possible. When no return value is set the function automatically returns null.