Edit: v4.11.8

Using the following script, on cc.Count()>0 with a non existent folder (as in a made up media ID) the output of cc.Count() = 1, and the script renders an empty <li> (as the macro is running as though it's true).

Is this an issue with 4.11.x? Or a global issue when using the media library?

@inherits umbraco.MacroEngines.DynamicNodeContext
@{
if ( String.IsNullOrEmpty(@Parameter.mediaFolder) ) {
    <div><p>A folder has not been selected</p></div>
}

var folder = Parameter.mediaFolder;
var media  = Model.MediaById(folder);

}

@helper traverse(dynamic node) {
var cc = node.Children;  
if (cc.Count()>0) {
    <ul>
        @foreach (var c in cc) {
            <li>
                @structure(c)
                @traverse(c)
            </li>
        }
    </ul>
}
 }
@helper structure( dynamic node ){
if ( node.NodeTypeAlias == "Folder" ) {
    <span class="folder" id="@node.Name.ToLower().Replace(" ", "_")">@node.Name</span>
} else {
    <a href="@node.Url" target="_blank">@node.Name</a>
}
}
<div class="formWrangler">
@traverse(media)
</div>