Wrong message is rendered for FormSavingNotification on CancelOperation

[jesperStoltDizparcHSTD]

Which Umbraco Forms version are you using? (Please write the exact version, example: 13.4.0)

16.2.0

Which Umbraco version are you using? (Please write the exact version, example: 13.5.2)

16.3.4

Issue summary

When adding a CancelOperation to an FormSaving notification with a subject and message it does not print the message but instead when you are trying to save the form.

An error occurred
Unknown error

It seams like the UmbracoForm save does note handle CancelOperations correctly.

Specifics

I have the same issue in bor Arc and Firefox

In the dev-console it prints the following error

[UmbTryExecuteController] Error in request: UmbApiError: Unknown error
    at y.mapToUmbError (index.js:335:186)
    at y.tryExecute (index.js:379:22)
    at async D (index.js:403:30)
    at async Hg.create (form-detail.server.data-source.ts:107:23)
    at async Kg.create (index.js:130:35)
    at async pe.submit (form-workspace.context.ts:166:7)
    at async pe.requestSave (form-workspace.context.ts:140:5)
    at async ds.execute (index.js:105:50)
    at async r.$ (workspace-action-default-kind.element-Cup7qCdo.js:67:7)

In the log-viewer it presents the following error

System.OperationCanceledException: Could not save form
   at Umbraco.Forms.Core.Services.BaseService`3.Insert(TType item)
   at Umbraco.Forms.Core.Services.FormService.Insert(Form item)
   at Umbraco.Forms.Web.Api.ManagementApi.Form.CreateFormController.Create(FormDesign formData)
   at lambda_method550(Closure, Object, Object[])
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.SyncActionResultExecutor.Execute(ActionContext actionContext, IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Logged|12_1(ControllerActionInvoker invoker)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|25_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
   at Umbraco.Cms.Web.Common.Middleware.BasicAuthenticationMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Umbraco.Cms.Api.Management.Middleware.BackOfficeExternalLoginProviderErrorMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Localization.RequestLocalizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at StackExchange.Profiling.MiniProfilerMiddleware.Invoke(HttpContext context) in C:\projects\dotnet\src\MiniProfiler.AspNetCore\MiniProfilerMiddleware.cs:line 112
   at Umbraco.Cms.Web.Common.Middleware.UmbracoRequestMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Umbraco.Cms.Web.Common.Middleware.UmbracoRequestMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Umbraco.Cms.Web.Common.Middleware.PreviewAuthenticationMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Umbraco.Cms.Web.Common.Middleware.UmbracoRequestLoggingMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at SixLabors.ImageSharp.Web.Middleware.ImageSharpMiddleware.Invoke(HttpContext httpContext, Boolean retry)
   at Umbraco.Forms.Web.HttpModules.ProtectFormUploadRequestsMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Umbraco.Cms.Api.Management.Middleware.BackOfficeAuthorizationInitializationMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

Steps to reproduce

1. Create an new Umbraco project
2. Add umbraco forms
3. Register an FormSavingNotification with below code

public class SaveNotification : INotificationHandler<FormSavingNotification>
{

    public void Handle(FormSavingNotification notification)
    {
        notification.CancelOperation(new EventMessage("Error", "Could not save form"));
    }
}

public class ConfigureUmbracoNotifications : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        builder.AddNotificationHandler<FormSavingNotification, SaveNotification>();
    }
}

4. Create an new form with any name
5. Press Save
6. It then prints the following error

An error occurred
Unknown error

Expected result / actual result

It prints an message with the following lines

Error
Could not save form

[acoumb]

Hi @jesperStoltDizparcHSTD ,

Thank you for raising this. I was able to replicate your use case, and it was added to our backlog for review in a coming sprint.

Adrian