stride3d/stride · error · ArgumentNullException

Value cannot be null. (Parameter 'part')

Error message

Value cannot be null. (Parameter 'part')

What it means

AssetPartCollection<TAssetPartDesign,TAssetPart>.Add(TAssetPartDesign) throws ArgumentNullException when the part design being added is null. The collection requires a non-null design carrying both a Part.Id and the part itself.

Solutions

1. Ensure the TAssetPartDesign instance is constructed before calling Add.
2. Check the data source producing null parts and skip or repair those entries.
3. Add a null check at the call site before invoking Add.

Example fix

// before
collection.Add(partDesign); // partDesign may be null
// after
if (partDesign != null) collection.Add(partDesign);

if (partDesign == null) return; // skip null part entries before Add

bool IsValidPart<TDesign>(TDesign? d) where TDesign : class => d is not null;

try { collection.Add(partDesign); } catch (ArgumentNullException) { log.Warning("Skipped null part design"); }

When it happens

Trigger: Calling assetPartCollection.Add(null), or Add(keyValuePair) where the KeyValuePair's Value is null (the Add(KeyValuePair<Guid,TAssetPartDesign>) path surfaces this as 'part').

Common situations: Populating an entity/prefab asset from data where a part entry failed to deserialize and is null; test code probing null handling (TestAddWithNullPartThrows).

Related errors

• The guid of the key does not match the guid of the value
• Cannot add an empty asset item reference
• Asset already exist in this collection
• Unable to find the base
• Unable to find the graph corresponding to the base part

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/408a8ef28dfdc27e. Report an issue: GitHub.

Appendix: source

Thrown at sources/assets/Stride.Core.Assets/AssetPartCollection.cs:15

// Copyright (c) .NET Foundation and Contributors (https://dotnetfoundation.org/ & https://stride3d.net) and Silicon Studio Corp. (https://www.siliconstudio.co.jp)
// Distributed under the MIT license. See the LICENSE.md file in the project root for more information.

using Stride.Core.Serialization;

namespace Stride.Core.Assets;

[DataSerializer(typeof(AssetPartCollectionSerializer<,>), Mode = DataSerializerGenericMode.GenericArguments)]
public sealed class AssetPartCollection<TAssetPartDesign, TAssetPart> : SortedList<Guid, TAssetPartDesign>
    where TAssetPartDesign : IAssetPartDesign<TAssetPart>
    where TAssetPart : IIdentifiable
{
    public void Add(TAssetPartDesign part)
    {
        if (part == null) throw new ArgumentNullException(nameof(part));
        Add(part.Part.Id, part);
    }

    public void Add(KeyValuePair<Guid, TAssetPartDesign> part)
    {
        if (part.Value == null) throw new ArgumentNullException(nameof(part));
        if (part.Key != part.Value.Part.Id) throw new ArgumentException(@"The guid of the key does not match the guid of the value", nameof(part));
        Add(part.Key, part.Value);
    }

    /// <summary>
    /// Refreshes the keys of this collection. Must be called if some ids of the contained parts have changed.
    /// </summary>
    public void RefreshKeys()
    {
        var values = Values.ToList();
        Clear();
        foreach (var value in values)

View on GitHub (pinned to 96fad776d2)