Identity error: Value cannot be null.\r\nParameter name: manager - asp.net-mvc

Question

I using ASP.NET Identity and when a user want to register get this error:
Value cannot be null.\r\nParameter name: manager.
Here is my Register Action code:
public virtual ActionResult Register(string nm, string em, string ps)
{
var redirectUrlPanel = new UrlHelper(Request.RequestContext).Action("Index", "HomeUsers", new { area = "Users" });
var redirectUrlAuction = new UrlHelper(Request.RequestContext).Action("Auction", "Default", new { area = "" });
if (ModelState.IsValid)
{
try
{
var user = new Q_Users();
user.UserName = nm;
user.Email = em;
user.SecurityStamp = Guid.NewGuid().ToString();
var adminresult = UserManager.Create(user, ps);
//Add User Admin to Role Admin
if (adminresult.Succeeded)
{
//Find Role Admin
var role = RoleManager.FindByName("Admin");
var result = UserManager.AddToRole(user.Id, role.Name);
if (result.Succeeded)
{
return Json(new { OK = "1", UrlPanel = redirectUrlPanel, UrlAuction = redirectUrlAuction });
}
}
else
{
return Json(new { OK = "0", UrlPanel = redirectUrlPanel, UrlAuction = redirectUrlAuction });
}
}
catch (Exception ex) { }
return Json(new { OK = "0", UrlPanel = redirectUrlPanel, UrlAuction = redirectUrlAuction });
}
else
{
return Json(new { OK = "0", UrlPanel = redirectUrlPanel, UrlAuction = redirectUrlAuction });
}
}
And the error in this Line: var adminresult = UserManager.Create(user, ps);

Answer 1

You are getting the error because the role manager was not initialized
To resolve this, follow the steps below
In the IdentityModels.cs file of the Models folder, Add the class below to the Models namespace.
public class ApplicationRole : IdentityRole
{
public ApplicationRole() : base() { }
public ApplicationRole(string name) : base(name) { }
}
In you IdentityConfig.cs file in App_Start folder, Add the class below
public class ApplicationRoleManager : RoleManager<ApplicationRole>
{
public ApplicationRoleManager(IRoleStore<ApplicationRole, string> roleStore)
: base(roleStore)
{
}
public static ApplicationRoleManager Create(IdentityFactoryOptions<ApplicationRoleManager> options, IOwinContext context)
{
return new ApplicationRoleManager(new RoleStore<ApplicationRole>(context.Get<ApplicationDbContext>()));
}
}
Go to Startup.Auth.cs file in the App_Start folder and add the code below to the ConfigureAuth Method.
app.CreatePerOwinContext<ApplicationRoleManager>(ApplicationRoleManager.Create);
You should stop getting the errors after this.
Hope this helps.