asp.net - MVC5 Using Controller to serve images, value can not be null -

i'm new mvc , followed tutorial on loading local files webpage , while seems work others getting error.

public class imagescontroller : controller {     // get: images     public actionresult someimage(string imagename)     {         var root = @"c:\images\";         var path = path.combine(root, imagename);         path = path.getfullpath(path);         if (!path.startswith(root))         {             // ensure serving file inside root folder             // , block requests outside "../web.config"             throw new httpexception(403, "forbidden");         }          return file(path, "image/png");     } } 

the error i'm getting is:

an exception of type 'system.argumentnullexception' occurred in mscorlib.dll not handled in user code additional information: value cannot null.

and line highlights is:

var path = path.combine(root, imagename);

when using url.action() helper, property name in anonymous object has match name of parameter in action.

and in case:

@url.action("someimage", "images", new { imagename = "logo.png" })