NullReferenceException: An exception occurred translating that FullConditionalExpression

[MaceWindu]

Ut-oh
An exception occurred translating that FullConditionalExpression. 

Please report this error with the stack trace below using https://github.com/agileobjects/ReadableExpressions/issues/new . 

Thanks! (and sorry about that)
Steve


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System.NullReferenceException: Object reference not set to an instance of an object. at
AgileObjects.ReadableExpressions.Translations.FixedValueTranslation.AgileObjects.ReadableExpressions.Translations.ITranslatable.get_TranslationSize() at AgileObjects.ReadableExpressions.Translations.CodeBlockTranslation.CalculateSizes() at
AgileObjects.ReadableExpressions.Translations.CodeBlockTranslation..ctor(ITranslation translation, ITranslationContext context) at
AgileObjects.ReadableExpressions.Extensions.PublicTranslationContextExtensions.GetCodeBlockTranslationFor(ITranslationContext context, Expression expression) at
AgileObjects.ReadableExpressions.Translations.ConditionalTranslation.TernaryTranslation..ctor(ConditionalExpression conditional, ITranslationContext context) at AgileObjects.ReadableExpressions.Translations.ConditionalTranslation.For(ConditionalExpression conditional, ITranslationContext context) at
AgileObjects.ReadableExpressions.Translations.ExpressionTranslation.GetTranslationFor(Expression expression) at AgileObjects.ReadableExpressions.Translations.ExpressionTranslation.GetTranslation() at
AgileObjects.ReadableExpressions.ExpressionExtensions.ToReadableString(Expression expression, Func`2 configuration) at
AgileObjects.ReadableExpressions.Visualizers.ObjectSource.ExpressionVisualizerObjectSource.GetTranslationFor(Object target) at
AgileObjects.ReadableExpressions.Visualizers.ObjectSource.ExpressionVisualizerObjectSource.GetData(Object target, Stream outgoingData, Action`2 serializer)

non-printed parameter is MySqlDecimal struct value (default)

[SteveWilkes]

Hi,

Thanks for reporting this!

Could you let me know - how is the default MySqlDecimal value being added to the Expression? I've tried a few ways (see e.g this DotNetFiddle) but can't reproduce the error, which is being thrown by the code trying to translate the default value in a way I wouldn't expect.

Cheers,

Steve

[MaceWindu]

looks like this one triggers it for me

MySqlDecimal val = default;
        var defaultDecimalConstant = Constant(val);

[SteveWilkes]

Ah yes, that does it - weird, cos if you switch MySqlDecimal to Guid, it works. I'll look into it...

[SteveWilkes]

Looks like MySqlDecimal.ToString() will return null from its default value (it just returns its underlying value), which it should never do.

I've updated the code to handle nulls returned from a ToString() call anyway - I guess someone could implement their own Extension Expression and return null for their own reasons, so it's better not to fall over.

Thanks again for letting me know about the issue.

[MaceWindu]

Actually, object.ToString has string? signature. A bit annoying, but null is valid case

https://github.com/dotnet/runtime/blob/main/src/libraries/System.Private.CoreLib/src/System/Object.cs#L39

[SteveWilkes]

Weird, Visual Studio seems to have a different opinion:

[MaceWindu]

that's because you have string as return type (overrides could have more strict return type)

[SteveWilkes]

Ahh, yes - good point. Still, if default(int?).ToString() returns an empty string instead of null, I think it's at least fair to say there's a convention of doing so.

In any case, the latest code handles nulls :)

[MaceWindu]

BTW, if you are interested in more details why ToString is nullable : https://github.com/dotnet/runtime/blob/main/docs/coding-guidelines/api-guidelines/nullability.md#virtualabstract-methods-and-interfaces

[SteveWilkes]

That's really interesting, thank you! :)