Description:
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In PHP 5.2.5, DOMDocument::saveXML() accepted null as it's first argument, which has this documentation:

Use this parameter to output only a specific node without XML declaration rather than the entire document. 

In PHP 5.2.6, passing null causes error.

Reproduce code:
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// $doc is a DOM document object.
return $doc->saveXML(null, LIBXML_NOEMPTYTAG);

Expected result:
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IMHO null is reasonable value, meaning that whole document should be saved. I suggest to fix this backward compatibility break.

Actual result:
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Catchable fatal error: Argument 1 passed to DOMDocument::saveXML() must be an instance of DOMNode, null given, called in ...\index.php on line 97 and defined in ...\inc.Menu.php on line 23