stride3d/stride · error · ArgumentException

Url must be valid, assign null instead

Error message

Url must be valid, assign null instead

What it means

BepuSimulation.AssociatedScene setter throws ArgumentException when assigned a UrlReference<Scene> that IsEmpty (default-constructed, pointing to no scene). Because a null assignment legitimately means 'no associated scene', the library forbids an empty URL value and instructs you to assign null instead.

Solutions

1. Assign null instead of an empty UrlReference<Scene> when you mean 'no scene'
2. Check value.IsEmpty in your own code before assigning and substitute null
3. Fill in the scene reference in the editor/Game Studio property so the URL is non-empty
4. If the value comes from deserialization, validate the source field for null/empty before constructing UrlReference<Scene>

Example fix

// before
simulation.AssociatedScene = new UrlReference<Scene>("", null); // IsEmpty == true
// after
simulation.AssociatedScene = string.IsNullOrEmpty(rawUrl) ? (UrlReference<Scene>?)null : new UrlReference<Scene>(rawUrl);

if (sceneUrl is UrlReference<Scene> u && u.IsEmpty)
    sceneUrl = null; // normalize empty URLs to null before assigning

bool IsValidSceneRef(UrlReference<Scene>? url) => url is null || !url.Value.IsEmpty;

try
{
    simulation.AssociatedScene = sceneUrl;
}
catch (ArgumentException ex) when (ex.Message.Contains("Url must be valid"))
{
    Logger.Warn("Empty scene URL assigned; defaulting to null");
    simulation.AssociatedScene = null;
}

When it happens

Trigger: Setting simulation.AssociatedScene = new UrlReference<Scene>() (default struct, no URL) or deserializing an entity whose scene URL field was left empty and then assigning it to the property.

Common situations: Wiring a BepuSimulation component in an editor/serializer where the scene picker was never filled in; constructing UrlReference<Scene> from an empty string; copying a component from another entity without the scene reference surviving serialization.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Mesh seems to have no volume; triangle rasterization…
• 's must be finite
• 's must be normalized
• 's must be finite and greater than zero
• Invalid Width/Height/Depth/ArraySize for Image 1D

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/de31b4ae7aa31acd. Report an issue: GitHub.

Appendix: source

Thrown at sources/engine/Stride.BepuPhysics/Stride.BepuPhysics/BepuSimulation.cs:89

    /// <summary>
    /// The scene associated with this simulation.
    /// </summary>
    /// <remarks>
    /// When this is set, entities spawning inside this scene will be automatically associated with
    /// this simulation as long as their <see cref="CollidableComponent.SimulationSelector"/> is set to <see cref="SceneBasedSimulationSelector"/>.
    /// See <see cref="SceneBasedSimulationSelector"/> for more info.
    /// </remarks>
    public UrlReference<Scene>? AssociatedScene
    {
        get
        {
            return _associatedScene;
        }
        set
        {
            if (value?.IsEmpty == true)
                throw new ArgumentException("Url must be valid, assign null instead");

            _associatedScene = value;
        }
    }

    /// <summary>
    /// The number of threads the simulation may use.
    /// </summary>
    /// <remarks>
    /// <see cref="Dispatcher.MaxDegreeOfParallelism"/> is the upper bound, -1 will default to that value.
    /// A value greater than <see cref="Dispatcher.MaxDegreeOfParallelism"/> will further split the work, potentially improving throughput depending on the context and simulation.
    /// </remarks>
    [Display(-1, "Thread Count")]
    public int ThreadCount
    {
        get;
        set
        {

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