[BUG] NumericValidationBehavior throws ArgumentNullException

[Niels-R]

Is there an existing issue for this?

• I have searched the existing issues

Did you read the "Reporting a bug" section on Contributing file?

• I have read the "Reporting a bug" section on Contributing file: https://github.com/CommunityToolkit/Maui/blob/main/CONTRIBUTING.md#reporting-a-bug

Current Behavior

Assume an Entry with the Flags property set to ValidateOnAttaching and Text bound to a nullable string property.
When loading the page view, an ArgumentNullException is thrown.

System.ArgumentNullException: Value cannot be null. (Parameter 'value')
   at System.ArgumentNullException.Throw(String paramName)
   at System.ArgumentNullException.ThrowIfNull(Object argument, String paramName)
   at CommunityToolkit.Maui.Behaviors.NumericValidationBehavior.ValidateAsync(String value, CancellationToken token) in /_/src/CommunityToolkit.Maui/Behaviors/Validators/NumericValidationBehavior.shared.cs:line 79
   at CommunityToolkit.Maui.Behaviors.ValidationBehavior`1[[System.String, System.Private.CoreLib, Version=10.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].ValidateAsync(Object value, CancellationToken token) in /_/src/CommunityToolkit.Maui/Behaviors/Validators/ValidationBehavior.shared.cs:line 463
   at CommunityToolkit.Maui.Behaviors.ValidationBehavior.UpdateStateAsync(VisualElement view, ValidationFlags flags, Boolean isForced, Nullable`1 parentToken) in /_/src/CommunityToolkit.Maui/Behaviors/Validators/ValidationBehavior.shared.cs:line 382

Expected Behavior

• No exception
• IsValid set to False

Steps To Reproduce

1. Open the project in the linked repository
2. Run the application in the Android emulator
3. Observe the exception being thrown on the loading of MainPage

Link to public reproduction project repository

https://github.com/Niels-R/ExceptionExample

Environment

- .NET MAUI CommunityToolkit: 13.0.0
- OS: macOS Tahoe 26.0.1 (25A362)
- .NET MAUI: 10.0.11

Anything else?

This bug has been reported before, but without a working sample to reproduce.

#979

[Niels-R]

I can confirm that the issue can also be reproduced in the iOS Simulator (using iPhone 14 device).

[bijington]

How does it behave if you call options.SetShouldSuppressExceptionsInBehaviors(true);?

[Niels-R]

Then the exception is suppressed (and logged to the debug console).

The exception is thrown in the NumericValidationBehaviour class on line 79 if value is null.

Maui/src/CommunityToolkit.Maui/Behaviors/Validators/NumericValidationBehavior.shared.cs

Line 79 in 4ed306b

ArgumentNullException.ThrowIfNull(value);

However, if you check the TextValidationBehavior class, you'll notice that it returns false when value is null.

Maui/src/CommunityToolkit.Maui/Behaviors/Validators/TextValidationBehavior.shared.cs

Line 162 in 4ed306b

value != null &&

(And also EmailValidationBehavior because it is derived from TextValidationBehavior...)

The same goes for the EmailValidationBehavior class.

Maui/src/CommunityToolkit.Maui/Behaviors/Validators/EmailValidationBehavior.shared.cs

Line 101 in 4ed306b

if (string.IsNullOrWhiteSpace(email)

I would expect consistent behaviour where false is returned when value is null for all validators and no need to suppress all exception in behaviours to avoid the application to crash.

What's your opinion?