stride3d/stride · error · ArgumentNullException

url cannot be null or empty.

Error message

url cannot be null or empty.

What it means

The protected UrlReferenceBase(string url) constructor requires a non-empty asset URL. Stride throws ArgumentNullException when the url parameter is null, empty, or whitespace, because a URL reference with no URL cannot point at any asset. It is a fail-fast guard for all concrete reference types (e.g. UrlReference<T>) deriving from UrlReferenceBase.

Solutions

1. Pass a valid, non-empty asset URL (e.g. relative to the virtual file system, like 'myScene.sdscene') to the reference constructor.
2. Check the source of the string before constructing: if it comes from a config/property lookup, handle the missing value before creating the reference.
3. If the reference is legitimately absent, keep the field null (UrlReference is a struct and default is valid) rather than constructing with an empty URL.

Example fix

// before
var reference = new UrlReference<Scene>(config.ScenePath); // throws if ScenePath null/empty
// after
if (!string.IsNullOrWhiteSpace(config.ScenePath))
    reference = new UrlReference<Scene>(config.ScenePath);

if (string.IsNullOrWhiteSpace(url))
    throw new ArgumentException("A non-empty asset URL is required to create a UrlReference.", nameof(url));
var reference = new UrlReference<Scene>(url);

static bool IsValidUrlReferenceSource(string? url) => !string.IsNullOrWhiteSpace(url);

When it happens

Trigger: Calling new UrlReference<T>(null), new UrlReference<T>(""), or new UrlReference<T>(" ") — any derived class constructor invoked with a null/whitespace url string, typically from deserialization or code building references programmatically.

Common situations: Constructing asset references in editor tooling or build scripts where the URL string comes from an uninitialized variable, a failed file-path lookup, or a properties file that omitted the asset path.

Related errors

• ArgumentNullException: value
• The asset directory cannot be null before deleting an asset.
• The given directory is not contained in the given package.
• Assets must have the same Id.
• Assets must have the same source.

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/22584ac0cc5b7a4a. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Serialization/Serialization/UrlReferenceBase.cs:33

public abstract class UrlReferenceBase : IReference, IUrlReference
{
    /// <summary>
    /// Create a new <see cref="UrlReferenceBase"/> instance.
    /// </summary>
    protected UrlReferenceBase()
    {
    }

    /// <summary>
    /// Create a new <see cref="UrlReferenceBase"/> instance.
    /// </summary>
    /// <param name="url"></param>
    /// <exception cref="ArgumentNullException">If <paramref name="url"/> is <c>null</c> or empty.</exception>
    protected UrlReferenceBase(string url)
    {
        if (string.IsNullOrWhiteSpace(url))
        {
            throw new ArgumentNullException(nameof(url), $"{nameof(url)} cannot be null or empty.");
        }

        this.Url = url;
    }

    /// <summary>
    /// Create a new <see cref="UrlReferenceBase"/> instance.
    /// </summary>
    /// <exception cref="ArgumentNullException">If <paramref name="url"/> is <c>null</c> or empty.</exception>
    protected UrlReferenceBase(AssetId id, string url)
    {
        if (string.IsNullOrWhiteSpace(url))
        {
            throw new ArgumentNullException(nameof(url), $"{nameof(url)} cannot be null or empty.");
        }

        this.Url = url;
        this.Id = id;

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