Surrounding ModelState with the newly introduced SimpleValidationModel type

src/Umbraco.Web.BackOffice/Controllers/AuthenticationController.cs

@@ -209,7 +209,7 @@ namespace Umbraco.Web.BackOffice.Controllers
             else
             {
                 AddModelErrors(result);
-                return new ValidationErrorResult(ModelState);
+                return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
             }
         }
 
@@ -470,7 +470,7 @@ namespace Umbraco.Web.BackOffice.Controllers
         {
             if (ModelState.IsValid == false)
             {
-                return new ValidationErrorResult(ModelState);
+                return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
             }
 
             var user = await _signInManager.GetTwoFactorAuthenticationUserAsync();

src/Umbraco.Web.BackOffice/Controllers/CurrentUserController.cs

@@ -185,7 +185,7 @@ namespace Umbraco.Web.BackOffice.Controllers
                 // so that is why it is being used here.
                 ModelState.AddModelError("value", result.Errors.ToErrorMessage());
 
-                return new ValidationErrorResult(ModelState);
+                return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
             }
 
             //They've successfully set their password, we can now update their user account to be approved

src/Umbraco.Web.BackOffice/Controllers/DataTypeController.cs

@@ -15,6 +15,7 @@ using Umbraco.Core.PropertyEditors;
 using Umbraco.Core.Security;
 using Umbraco.Core.Serialization;
 using Umbraco.Core.Services;
+using Umbraco.Extensions;
 using Umbraco.Web.BackOffice.Filters;
 using Umbraco.Web.Common.ActionsResults;
 using Umbraco.Web.Common.Attributes;
@@ -302,7 +303,7 @@ namespace Umbraco.Web.BackOffice.Controllers
             catch (DuplicateNameException ex)
             {
                 ModelState.AddModelError("Name", ex.Message);
-                return new ValidationErrorResult(ModelState);
+                return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
             }
 
             // map back to display model, and return

src/Umbraco.Web.BackOffice/Controllers/DictionaryController.cs

@@ -15,6 +15,7 @@ using Constants = Umbraco.Core.Constants;
 using Umbraco.Core.Configuration.Models;
 using Microsoft.Extensions.Options;
 using Microsoft.AspNetCore.Authorization;
+using Umbraco.Extensions;
 using Umbraco.Web.Common.ActionsResults;
 using Umbraco.Web.Common.Authorization;
 
@@ -224,7 +225,7 @@ namespace Umbraco.Web.BackOffice.Controllers
                         userCulture,
                         new Dictionary<string, string> { { "0", dictionary.Name } });
                     ModelState.AddModelError("Name", message);
-                    return new ValidationErrorResult(ModelState);
+                    return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
                 }
 
                 dictionaryItem.ItemKey = dictionary.Name;

src/Umbraco.Web.BackOffice/Controllers/LanguageController.cs

@@ -10,6 +10,7 @@ using Umbraco.Core.Configuration.Models;
 using Umbraco.Core.Mapping;
 using Umbraco.Core.Models;
 using Umbraco.Core.Services;
+using Umbraco.Extensions;
 using Umbraco.Web.Common.ActionsResults;
 using Umbraco.Web.Common.Attributes;
 using Umbraco.Web.Common.Authorization;
@@ -114,7 +115,7 @@ namespace Umbraco.Web.BackOffice.Controllers
         public ActionResult<Language> SaveLanguage(Language language)
         {
             if (!ModelState.IsValid)
-                return new ValidationErrorResult(ModelState);
+                return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
 
             // this is prone to race conditions but the service will not let us proceed anyways
             var existingByCulture = _localizationService.GetLanguageByIsoCode(language.IsoCode);
@@ -130,7 +131,7 @@ namespace Umbraco.Web.BackOffice.Controllers
             {
                 //someone is trying to create a language that already exist
                 ModelState.AddModelError("IsoCode", "The language " + language.IsoCode + " already exists");
-                return new ValidationErrorResult(ModelState);
+                return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
             }
 
             var existingById = language.Id != default ? _localizationService.GetLanguageById(language.Id) : null;
@@ -147,7 +148,7 @@ namespace Umbraco.Web.BackOffice.Controllers
                 catch (CultureNotFoundException)
                 {
                     ModelState.AddModelError("IsoCode", "No Culture found with name " + language.IsoCode);
-                    return new ValidationErrorResult(ModelState);
+                    return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
                 }
 
                 // create it (creating a new language cannot create a fallback cycle)
@@ -170,7 +171,7 @@ namespace Umbraco.Web.BackOffice.Controllers
             if (existingById.IsDefault && !language.IsDefault)
             {
                 ModelState.AddModelError("IsDefault", "Cannot un-default the default language.");
-                return new ValidationErrorResult(ModelState);
+                return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
             }
 
             existingById.IsDefault = language.IsDefault;
@@ -185,12 +186,12 @@ namespace Umbraco.Web.BackOffice.Controllers
                 if (!languages.ContainsKey(existingById.FallbackLanguageId.Value))
                 {
                     ModelState.AddModelError("FallbackLanguage", "The selected fall back language does not exist.");
-                    return new ValidationErrorResult(ModelState);
+                    return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
                 }
                 if (CreatesCycle(existingById, languages))
                 {
                     ModelState.AddModelError("FallbackLanguage", $"The selected fall back language {languages[existingById.FallbackLanguageId.Value].IsoCode} would create a circular path.");
-                    return new ValidationErrorResult(ModelState);
+                    return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
                 }
             }
 

src/Umbraco.Web.BackOffice/Controllers/PackageController.cs

@@ -10,9 +10,11 @@ using Microsoft.Net.Http.Headers;
 using Semver;
 using Umbraco.Core;
 using Umbraco.Core.Hosting;
+using Umbraco.Core.Models;
 using Umbraco.Core.Models.Packaging;
 using Umbraco.Core.Security;
 using Umbraco.Core.Services;
+using Umbraco.Extensions;
 using Umbraco.Web.Common.ActionsResults;
 using Umbraco.Web.Common.Attributes;
 using Umbraco.Web.Common.Authorization;
@@ -67,7 +69,7 @@ namespace Umbraco.Web.BackOffice.Controllers
         public ActionResult<PackageDefinition> PostSavePackage(PackageDefinition model)
         {
             if (ModelState.IsValid == false)
-                return new ValidationErrorResult(ModelState);
+                return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
 
             //save it
             if (!_packagingService.SaveCreatedPackage(model))

src/Umbraco.Web.BackOffice/Controllers/UsersController.cs

@@ -704,7 +704,7 @@ namespace Umbraco.Web.BackOffice.Controllers
                 ModelState.AddModelError(memberName, passwordChangeResult.Result.ChangeError.ErrorMessage);
             }
 
-            return new ValidationErrorResult(ModelState);
+            return new ValidationErrorResult(new SimpleValidationModel(ModelState.ToErrorDictionary()));
         }