Empty conditional processing attributes should be preserved
to hide elements

===

<svg xmlns="http://www.w3.org/2000/svg">
    <g requiredFeatures=""/>
    <g requiredExtensions=""/>
    <g systemLanguage=""/>
</svg>

@@@

<svg xmlns="http://www.w3.org/2000/svg">
    <g requiredFeatures=""/>
    <g requiredExtensions=""/>
    <g systemLanguage=""/>
</svg>