stride3d/stride · error · InvalidOperationException

[ ] cannot be null in

Error message

[{nameof(Description)}] cannot be null in {GetType().Name}

What it means

TemplateGeneratorParameters.ValidateParameters throws this InvalidOperationException when the Description property — the TemplateDescription describing which template to run — is null. Without a description the generator cannot know what files to produce or what scope applies, so validation rejects the parameters before any generation starts.

Solutions

1. Assign a valid TemplateDescription to the Description property before calling Validate().
2. Load the description through the TemplateManager/template provider for the template Id you intend to run and check it is non-null.
3. If constructing descriptions by hand, ensure you pass it into the parameters object rather than only keeping it locally.

Example fix

// before
var p = new SessionTemplateGeneratorParameters { Name = "MyGame", OutputDirectory = dir, Logger = logger, Session = session };
p.Validate(); // throws: Description null

// after
var desc = TemplateManager.FindTemplate(templateId); // non-null TemplateDescription
var p = new SessionTemplateGeneratorParameters { Name = "MyGame", OutputDirectory = dir, Description = desc, Logger = logger, Session = session };
p.Validate();

if (p.Description == null)
    throw new ArgumentException("TemplateGeneratorParameters.Description must be set to the resolved TemplateDescription before Validate().");

bool HasDescription(TemplateGeneratorParameters p) => p.Description is not null;

try { p.Validate(); }
catch (InvalidOperationException ex) when (ex.Message.Contains(nameof(TemplateGeneratorParameters.Description)))
{
    // re-resolve the template by Id and retry
}

When it happens

Trigger: Calling Validate() on any TemplateGeneratorParameters-derived object where Description was never assigned. Note the preceding OutputDirectory check dereferences Description, so a null Description with a null OutputDirectory throws the OutputDirectory error first; setting OutputDirectory (or a session-scope description) exposes this null-Description error.

Common situations: Manually constructed parameters in unit tests or tooling that only set Name/Logger; loading templates via a template provider that failed silently and returned no TemplateDescription; forgetting to assign Description while copying all other fields to a new parameters object.

Related errors

• [ ] cannot be null in
• [ ] cannot be null in
• [ ] cannot be null in
• [ ] cannot be null in
• [ ] cannot be null in

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/cee939ffd874b1f5. Report an issue: GitHub.

Appendix: source

Thrown at sources/assets/Stride.Core.Assets/Templates/TemplateGeneratorParameters.cs:227

    public void SetTag<T>(PropertyKey<T> key, T value)
    {
        Tags[key] = value;
    }

    protected virtual void ValidateParameters()
    {
        if (Name == null)
        {
            throw new InvalidOperationException($"[{nameof(Name)}] cannot be null in {GetType().Name}");
        }
        if (OutputDirectory == null && Description.Scope == TemplateScope.Session)
        {
            throw new InvalidOperationException($"[{nameof(OutputDirectory)}] cannot be null in {GetType().Name}");
        }
        if (Description == null)
        {
            throw new InvalidOperationException($"[{nameof(Description)}] cannot be null in {GetType().Name}");
        }
        if (Logger == null)
        {
            throw new InvalidOperationException($"[{nameof(Logger)}] cannot be null in {GetType().Name}");
        }
    }
}

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