fix some issue and cover by test (#669)

src/Web/ViewModels/Manage/IndexViewModel.cs

@@ -4,7 +4,7 @@ namespace Microsoft.eShopWeb.Web.ViewModels.Manage;
 
 public class IndexViewModel
 {
-    public string Username { get; set; }
+    public string? Username { get; set; }
 
     public bool IsEmailConfirmed { get; set; }
 
@@ -16,5 +16,5 @@ public class IndexViewModel
     [Display(Name = "Phone number")]
     public string PhoneNumber { get; set; }
 
-    public string StatusMessage { get; set; }
+    public string? StatusMessage { get; set; }
 }