Static string return a value problem

 Hello, i have a problem with a static string that return a value.
  
public static string Files
{
get
{
DirectoryInfo dir = new DirectoryInfo(HttpContext.Current.Request.QueryString["show"]);
if (dir != null)
{
if (dir.Name.EndsWith(".png") || dir.Name.EndsWith(".jpeg") || dir.Name.EndsWith(".jpg") || dir.Name.EndsWith(".gif"))
{
return "Bild";
}
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