stride3d/stride · error · InvalidOperationException

[ ] cannot be null in

Error message

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

What it means

PackageTemplateGeneratorParameters.ValidateParameters throws this InvalidOperationException when the Package property — the Stride Package in which the template generator executes — is null. A package-scoped template needs a target package to modify or add projects to, so validation fails fast during Validate() instead of crashing inside the generator with a NullReferenceException.

Solutions

1. Assign a valid Package instance to the Package property before calling Validate().
2. Resolve the target package from the loaded session, e.g. session.Packages.Find(...), or load it with Package.Load.
3. If you meant to generate without a package, use SessionTemplateGeneratorParameters (session scope) instead.

Example fix

// before
var p = new AssetTemplateGeneratorParameters(targetLocation)
{
    Name = "MySprite",
    Description = desc,
    Logger = logger
    // Package never set
};
p.Validate(); // throws

// after
p.Package = session.CurrentPackage; // or Package.Load(packagePath, logger)
p.Validate();

if (p is PackageTemplateGeneratorParameters pp && pp.Package == null)
    throw new InvalidOperationException("Package must be resolved from the session (or loaded) before Validate().");

bool HasPackage(PackageTemplateGeneratorParameters p) => p.Package is not null;

try { p.Validate(); }
catch (InvalidOperationException ex) when (ex.Message.Contains(nameof(PackageTemplateGeneratorParameters.Package)))
{
    // resolve the target Package and retry
}

When it happens

Trigger: Calling Validate() on a PackageTemplateGeneratorParameters (or AssetTemplateGeneratorParameters, which inherits the check) whose Package property was never assigned — e.g. constructed via the default constructor and only Name/Description/Logger were set.

Common situations: Tooling that generates assets or packages into a currently open Stride project but never resolves the Package object from the session; passing a null package through the PackageTemplateGeneratorParameters(parameters, package) constructor; scripts running outside the editor without loading the package.

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/2e84cb89468a0fd7. Report an issue: GitHub.

Appendix: source

Thrown at sources/assets/Stride.Core.Assets/Templates/TemplateGeneratorParameters.cs:59

        Package = package;
    }
    /// <summary>
    /// Gets or sets the package in which to execute this template
    /// </summary>
    /// <value>The package.</value>
    public Package Package { get; set; }

    protected override void ValidateParameters()
    {
        base.ValidateParameters();

        if (Description.Scope != TemplateScope.Package && GetType() == typeof(PackageTemplateGeneratorParameters))
        {
            throw new InvalidOperationException($"[{nameof(Description)}.{nameof(Description.Scope)}] must be {TemplateScope.Package} in {GetType().Name}");
        }
        if (Package == null)
        {
            throw new InvalidOperationException($"[{nameof(Package)}] cannot be null in {GetType().Name}");
        }
    }
}

public class AssetTemplateGeneratorParameters : PackageTemplateGeneratorParameters
{
    public AssetTemplateGeneratorParameters(UDirectory targetLocation, IEnumerable<UFile>? sourceFiles = null)
    {
        TargetLocation = targetLocation;
        SourceFiles = [];
        if (sourceFiles != null)
            SourceFiles.AddRange(sourceFiles);
    }

    public UDirectory TargetLocation { get; }

    public List<UFile> SourceFiles { get; }

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