asp.net mvc - Passing a list of model object to my action method using Radio Buttons -

i have entity securityroletypepermision stores 3 ids values:-

• securityroleid
• assettypeid
• permissionlevelid

i working on security matrix inside asp.net mvc web application should populate database table.

my view looks as:-

model tms.viewmodels.securityrolegroupassign @using (html.beginform("assign","securityrole")) { @html.antiforgerytoken() @html.validationsummary(true) <table class="table table-striped table-bordered bootstrap-datatable datatable">  <thead><tr> <th></th> @foreach(var item in model.permisionlevel.orderbydescending(a=>a.permisionsize)){         <th> @item.name @html.hiddenfor(model => item.permisionlevelid)         </th>}     </tr> @foreach (var item2 in model.technologytype.orderby(a=>a.name)) {    <tr>     <td class="f">         @item2.name     </td>        @foreach (var item3 in model.permisionlevel.orderbydescending(a=>a.permisionsize))        {            <td class="f">                @html.radiobuttonfor(model => item2.assettypeid,item2.assettypeid.tostring())                @html.hiddenfor(model => item3.permisionlevelid,item3.permisionlevelid)            </td>} </tr>} @html.hiddenfor(model => model.securityrole.securityroleid) </table></div></div></div>  <p><input type="submit" value="save" /> </p> 

my action method is:-

[httppost] public actionresult assign(ilist<securityroletypepermision> list)         {    foreach (var c in list)             {  repository.insertorupdatesecurityroletypepermisions(c);             }             repository.save();             return redirecttoaction("index");} 

currently facing following problems:-

1. if submit form following error inside assign action method:-

system.nullreferenceexception unhandled user code

2. all radio buttons inside same group user can select 1 radio button, per table. instead need user able select 1 radio button each table row.

   thanks

::::::edit:::::::

the viewmodel :-

public class securityrolegroupassign {     public  ienumerable<technologytype> technologytype {get; set;}     public  ienumerable<permisionlevel> permisionlevel {get; set;}     public securityrole securityrole { get; set; }  } 

part of database is:-