Dear All
I tried to get the tabID to move one customer module to another, for this i wrote the below code and I got an error Object reference null in the below red line any one have any idea about it why it's giving this error and how to fixed it 

using DotNetNuke.Entities.Modules;
using DotNetNuke.Entities.Tabs;
using System.Collections;
using System.Collections.Generic;

 public int findPageTabId(string friendlyName, int portalId)

        {
            int returnValue =0; 
            ModuleController moduleController = new ModuleController();
            int myModuleDefId = Convert.ToInt16(DesktopModuleController.GetDesktopModuleByFriendlyName(friendlyName).DesktopModuleID);
            ArrayList tabs = new ArrayList((new TabController()).GetTabsByPortal(portalId));
            foreach (TabInfo ti in tabs)
            {
                Dictionary modules = moduleController.GetTabModules(ti.TabID);
                foreach (ModuleInfo mi in modules.Values)
                {
                    // If the module on the page is the module we
                    // are looking for, return it.
                    if (mi.DesktopModuleID == myModuleDefId)
                    {
                        returnValue =  ti.TabID;
                    }
                }
            }


            return returnValue; 

        }