Description:
------------
In addition to https://bugs.php.net/bug.php?id=80537

The signature for the following methods :

* hasAttributeNS
* getAttributeNS
* setAttributeNS
* removeAttributeNS
* getAttributeNodeNS

Report their first argument as a nullable string. This is not what is documented and passing null as the first argument to these method do throw a TypeError.

Test script:
---------------
<?php declare(strict_types=1);

$el = new class('foo') extends DOMElement {
  public function hasAttributeNS(string $namespace , string $localName): bool {
    return true;
  }
};

$el = new class('foo') extends DOMElement {
  public function getAttributeNS(string $namespace , string $localName): string {
    return 'bar';
  }
};

$el = new class('foo') extends DOMElement {
  public function setAttributeNS(string $namespace, string $qualifiedName, string $value): void {}
};

// etc...

Actual result:
--------------
PHP Fatal error:  Declaration of DOMElement@anonymous::hasAttributeNS(string $namespaceURI, string $localName): bool must be compatible with DOMElement::hasAttributeNS(?string $namespace, string $localName) in ...

PHP Fatal error:  Declaration of DOMElement@anonymous::getAttributeNS(string $namespaceURI, string $localName): string must be compatible with DOMElement::getAttributeNS(?string $namespace, string $localName) in ...

PHP Fatal error:  Declaration of DOMElement@anonymous::setAttributeNS(string $namespace, string $qualifiedName, string $value): void must be compatible with DOMElement::setAttributeNS(?string $namespace, string $qualifiedName, string $value) in ...

// etc...