Allow short ternary operator for boolean

[LastDragon-ru]

Disallow short ternary operator (?:) - implies weak comparison, it's recommended to use null coalesce operator (??) or ternary operator with strict condition.

It is not the case if the left value is always boolean, right?

$a = false;      // boolean
$b = $a ?: null; // much more readable than
$c = $a !== false ? true : null;