VarTag::initialize function wrong parse regex

[xbg]

According to the documentation $element_name is optional

But regex and logic in VarTag::initialize requires it.

Current VarTag variant can't parse first example from documentation

class Foo
{
  /** @var string|null Should contain a description */
  protected $description = null;
}

[tshakah]

There is a PR for this - is there any chance it can get merged?