Create a valid but empty OPML file.
Path to empty OPML file.
function getEmptyOpml() {
$opml = <<<EOF
<?xml version="1.0" encoding="utf-8"?>
<opml version="1.0">
<head></head>
<body>
<outline text="Sample text" />
<outline text="Sample text" url="Sample URL" />
</body>
</opml>
EOF;
$path = 'public://empty-opml.xml';
return file_unmanaged_save_data($opml, $path);
}