ViewBag losing reference after submitting form. Asp.Net MVC

Hello, I have two ViewBags that are storing a list each, I load them into a form to make a select box, next to them has a Remove button. So far so good, but when I click the first ViewBag button, a reference loss error occurs, the second ViewBag is working 100% perfect.

View:

<label>Especializações:</label>
@{
    if (((List<ProfessionalSpecialization>)ViewBag.ListProfessionalSpecialization).Count > 0)
    {
        using (Html.BeginForm("RemoveProfessionalUserSpecializations", "ProfessionalUser", FormMethod.Post, new { enctype = "multipart/form-data" }))
        {
            <div class="col-lg-6" style="display:inline">
                <nav class="mainmenu" style="width: 246px; margin: auto; position: relative; max-width: 100%;">
                    <select id="specialization" class="form-control" name="specialization">
                        @foreach (ProfessionalSpecialization item in (List<ProfessionalSpecialization>)ViewBag.ListProfessionalSpecialization)
                        {
                            <option>@item.Title</option>
                        }
                    </select>
                    <button type="submit" class="btn btn-primary">Remover</button>
                </nav>
            </div>
        }
    }
    else
    {
        <label>Você não possui especializações cadastradas.</label>
    }
}
<label>Áreas:</label>
@{
    if (((List<ProfessionalType>)ViewBag.ListProfessionalType).Count > 0)
    {
        using (Html.BeginForm("RemoveProfessionalUserTypes", "ProfessionalUser", FormMethod.Post, new { enctype = "multipart/form-data" }))
        {
            <div class="col-lg-6" style="display:inline">
                <nav class="mainmenu" style="width: 246px; margin: auto; position: relative; max-width: 100%;">
                    <select id="type" class="form-control" name="type">
                        @foreach (ProfessionalType item in (List<ProfessionalType>)ViewBag.ListProfessionalType)
                        {
                            <option>@item.Title</option>
                        }
                    </select>
                    <button type="submit" class="btn btn-primary">Remover</button>
                </nav>
            </div>
        }
    }
    else
    {
        <label>Você não possui áreas cadastradas.</label>
    }
}

What happens is that if you clicked on the submit of the second form, it follows okay, if clicked on the first, the following error occurs:

  

Object reference not set to an instance of an object.   if (((List) ViewBag.ListProfessionalSpecialization) .Count> 0)

Controller:

public ActionResult Edit(int id)
{
    ProfessionalUser pUser = new ProfessionalUser();
    using (ProfessionalUserDAO pUserDAO = new ProfessionalUserDAO())
    {
        pUser = pUserDAO.ListProfessionalUserById(id);
    }
    List<ProfessionalSpecialization> listSpecializationsOfUser = new List<ProfessionalSpecialization>();
    List<ProfessionalSpecialization> listAllSpecializations = new List<ProfessionalSpecialization>();
    List<ProfessionalType> listTypesOfUser = new List<ProfessionalType>();
    List<ProfessionalType> listAllTypes = new List<ProfessionalType>();

    using (ProfessionalUserDAO dao = new ProfessionalUserDAO())
    {
        try
        {
            using (ProfessionalSpecializationDAO sDAO = new ProfessionalSpecializationDAO())
            {
                listAllSpecializations = sDAO.ListProfessionalSpecialization(0);
                foreach (int idToGetSpecialization in pUser.Specializations)
                {
                    listSpecializationsOfUser.Add(sDAO.ListProfessionalSpecializationById(idToGetSpecialization));
                }
            }

            using (ProfessionalTypeDAO tDAO = new ProfessionalTypeDAO())
            {
                listAllTypes = tDAO.ListProfessionalType(0);
                foreach (int idToGetType in pUser.Types)
                {
                    listTypesOfUser.Add(tDAO.ListProfessionalTypeById(idToGetType));
                }
            }

            ViewBag.ListAllSpecializations = listAllSpecializations;
            ViewBag.ListProfessionalSpecialization = listSpecializationsOfUser;
            ViewBag.ListAllTypes = listAllTypes;
            ViewBag.ListProfessionalType = listTypesOfUser;
            return View(ProfessionalUser.UserLogged);
        }
        catch (Exception)
        {
            return HttpNotFound();
        }
    }
}

Actions that go to forms:

[Authorize]
[HttpPost]
public ActionResult RemoveProfessionalUserSpecializations(FormCollection form)
{
    if (ModelState.IsValid && form != null)
    {
        string spec = form["specialization"].ToString();
        using (ProfessionalUserDAO dao = new ProfessionalUserDAO())
        {
            dao.RemoveSpecializationFromUser(spec);
        }
    }
    return RedirectToAction("Edit", new { id = ProfessionalUser.UserLogged.IdProfessionalUser });
}

[Authorize]
[HttpPost]
public ActionResult RemoveProfessionalUserTypes(FormCollection form)
{
    if (ModelState.IsValid && form != null)
    {
        string type = form["type"].ToString();
        using (ProfessionalUserDAO dao = new ProfessionalUserDAO())
        {
            dao.RemoveTypeFromUser(type);
        }
    }
    return RedirectToAction("Edit", new { id = ProfessionalUser.UserLogged.IdProfessionalUser });
}