Getting a null reference exception in the controller for checkbox in ASP.NET MVC

@model WebApplication3.student1

@{
    ViewBag.Title = "Create";
}

<h2>Create</h2>


@using (Html.BeginForm("Create", "student1", FormMethod.Post, new { enctype = "multipart/form-data" }))
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <h4>Registration Form for Students</h4>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        @*<div class="form-group">
                @Html.LabelFor(model => model.student_id, htmlAttributes: new { @class = "control-label col-md-2" })
                <div class="col-md-10">
                    @Html.EditorFor(model => model.student_id, new { htmlAttributes = new { @class = "form-control" } })
                    @Html.ValidationMessageFor(model => model.student_id, "", new { @class = "text-danger" })
                </div>
            </div>*@

        <div class="form-group">
            @Html.LabelFor(model => model.Name, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Name, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Name, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.Last_name, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Last_name, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Last_name, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.age, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.age, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.age, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.phone, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.phone, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.phone, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.email, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.email, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.email, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.gender, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
            @Html.LabelFor(model => model.gender, "Male:")
            @Html.RadioButtonFor(model => model.gender, "Male")
            @Html.LabelFor(model => model.gender, "Female:")
            @Html.RadioButtonFor(model => model.gender, "Female")
            @Html.LabelFor(model => model.gender, "Others:")
            @Html.RadioButtonFor(model => model.gender, "Others")
            @Html.ValidationMessageFor(model => model.gender, "", new { @class = "text-danger" })
        </div>

            
                   
               
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.dob, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.dob, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.dob, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.hobbies, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
              
                @foreach (var item in ViewBag.hobby)
                {
                    <input type="checkbox" name="hobb" value="@item.Value" />@item.Text
                }
                @*@Html.EditorFor(model => model.hobbies, new { htmlAttributes = new { @class = "form-control" } })*@

                @*@Html.CheckBoxFor(model => model.hobbies,true)*@
                @*@Html.LabelFor(model => model.hobbies, "Singing")
                @Html.CheckBoxFor(model => model.hobbies, "Singing")
                @Html.LabelFor(model => model.hobbies, "Reading")
                @Html.CheckBoxFor(model => model.hobbies, "Reading")
                @Html.LabelFor(model => model.hobbies, "Dancing")
                @Html.CheckBoxFor(model => model.hobbies, "Dancing")*@



            </div>
        </div>

        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Create" class="btn btn-default" />
            </div>
        </div>
    </div>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Entity;
using System.Linq;
using System.Net;
using System.Web;
using System.Web.Mvc;
using WebApplication3;

namespace WebApplication3.Controllers
{
    public class student1Controller : Controller
    {
        private preet_testEntities db = new preet_testEntities();

        // GET: student1
        public ActionResult Index()
        {
           

            return View(db.student1.ToList());


        }
        //[HttpPost]
        //public string Index1(IEnumerable<student1> students)
        //{
        //    if (students.Count(x => x.hobbies) == 0)
        //    {
        //        return "please select a value";
        //    }
        //}
        // GET: student1/Details/5
        public ActionResult Details(int? id)
        {
            if (id == null)
            {
                return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
            }
            student1 student1 = db.student1.Find(id);
            if (student1 == null)
            {
                return HttpNotFound();
            }
            return View(student1);
        }

        // GET: student1/Create
        public ActionResult Create()
        {
            var list = new SelectList(new[]
                                             {
                                              new {ID="Reading",Name="Reading"},
                                              new{ID="Writing",Name="Writing"}
                                          },
                               "ID", "Name", 1);
            ViewBag.hobby = list;
            return View();
        }

        // POST: student1/Create
        // To protect from overposting attacks, enable the specific properties you want to bind to, for 
        // more details see https://go.microsoft.com/fwlink/?LinkId=317598.
        [HttpPost]
        [ValidateAntiForgeryToken]
        
        public ActionResult Create(student1 student1,FormCollection fc)
        {
            if (ModelState.IsValid)
            {
                
                student1 obj = db.student1.Find(student1.student_id);

                obj.hobbies = fc["hobb"] != null ? fc["hobb"].ToString() : obj.hobbies; //the above line is where the error occurs.
                db.SaveChanges();
                  ViewBag.hobby=obj.hobbies;
                return RedirectToAction("Index");
            }

            return View(student1);
        }

        // GET: student1/Edit/5
        public ActionResult Edit(int? id)
        {

            if (id == null)
            {
                return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
            }
            student1 student1 = db.student1.Find(id);
            if (student1 == null)
            {
                return HttpNotFound();
            }
            var list = new SelectList(new[]
                                             {
                                              new {ID="Reading",Name="Reading"},
                                              new{ID="Writing",Name="Writing"}
                                          },
                               "ID", "Name", 1);
            ViewBag.hobby = list;
            
            return View(student1);
        }

        // POST: student1/Edit/5
        // To protect from overposting attacks, enable the specific properties you want to bind to, for 
        // more details see https://go.microsoft.com/fwlink/?LinkId=317598.
        [HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult Edit( student1 student1 ,FormCollection fc)
        {
            if (ModelState.IsValid)
            {
                student1.hobbies = fc["hobb"].ToString(); 
                db.Entry(student1).State = EntityState.Modified;
                db.SaveChanges();
                return RedirectToAction("Index");
            }
            return View(student1);
        }

        // GET: student1/Delete/5
        public ActionResult Delete(int? id)
        {
            if (id == null)
            {
                return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
            }
            student1 student1 = db.student1.Find(id);
            if (student1 == null)
            {
                return HttpNotFound();
            }
            return View(student1);
        }

        // POST: student1/Delete/5
        [HttpPost, ActionName("Delete")]
        [ValidateAntiForgeryToken]
        public ActionResult DeleteConfirmed(int id)
        {
            student1 student1 = db.student1.Find(id);
            db.student1.Remove(student1);
            db.SaveChanges();
            return RedirectToAction("Index");
        }

        protected override void Dispose(bool disposing)
        {
            if (disposing)
            {
                db.Dispose();
            }
            base.Dispose(disposing);
        }
    }
}