explicit null check

Author: shmax

src/Ast/PhpDoc/TemplateTagValueNode.php

@@ -26,7 +26,7 @@ public function __construct(string $name, ?TypeNode $bound, string $description)
 
 	public function __toString(): string
 	{
-		$bound = isset($this->bound) ? " of {$this->bound}" : '';
+		$bound = $this->bound !== null ? " of {$this->bound}" : '';
 		return trim("{$this->name}{$bound} {$this->description}");
 	}