asp.net mvc - How to compare viewbag value with model another value in mvc 4 -

i trying send viewbag action method view. when first page loads viewbag value null. when call checkpermissions action method viewbag gets value , return same view time viewbag contains value , want compare viewbag value value. tried following error appearing. cannot perform runtime binding on null reference. index view code.

@model c3card.models.grouppermissionvm @{     viewbag.title = "index"; } @using (html.beginform()) {   @html.labelfor(m=>m.groupid)   @html.dropdownlistfor(m => m.groupid, model.grouplist, "please select", new { id = "ddlgrp" })     foreach(var permission in model.permissions)     {         if (viewbag.marlid.equals(permission))         {         <label>             @html.radiobuttonfor(m => m.perm_id, permission.perm_id, new {@checked="true"})             <span>@permission.perm_levelname</span>         </label>         }         else         {             <label>             @html.radiobuttonfor(m => m.perm_id, permission.perm_id)             <span>@permission.perm_levelname</span>         </label>          }     } 

this action method

public actionresult checkpermissions(int id)         {             var groups = db.tm_grp_group.where(a => a.grp_isactive == true);             var permissions = db.tm_perm_level;             grouppermissionvm model = new grouppermissionvm             {                marlid=db.ts_grp_perm_mapping.select(p=>p.grp_id==id).count(),                 grouplist = new selectlist(groups, "grp_id", "grp_name"),                 permissions = permissions.select(p => new permissionvm                 {                     perm_id = p.perm_id,                     perm_levelname = p.perm_levelname                  })             };           viewbag.marlid = db.ts_grp_perm_mapping.select(p => p.grp_id == id).count();              return view("index",model);         } 

any suggestion why not able compare values inside if condition? in advance. line causing me error if (viewbag.marlid.equals(permission)) edited follows

foreach(var permission in model.permissions)     {        if(model.marlid==permission.perm_id)        {           <label>             @html.radiobuttonfor(m => m.perm_id, permission.perm_id,new { @checked = true } )@model.marlid.tostring()             <span>@permission.perm_levelname</span>         </label>         } 

you can change code given below

if(viewbag.marlid != null && model.permissions != null)     {         foreach(var permission in model.permissions)         {            if(viewbag.marlid == permission.perm_id)            {               <label>                 @html.radiobuttonfor(m => m.perm_id, permission.perm_id,new { @checked = true } )@model.marlid.tostring()                 <span>@permission.perm_levelname</span>             </label>            }         }     } 

hope helps.