CoplayDev/unity-mcp · error · ArgumentException

Screenshotter cannot be null

Error message

Screenshotter cannot be null

What it means

Thrown by TypePreviewGeneratorFromScene.ValidateSettings when Settings.Screenshotter is null. The scene-based preview generator requires a screenshotter instance to capture previews of objects in a scene. This validation runs after the base class InputPaths/OutputPath checks.

Source

Thrown at TestProjects/AssetStoreUploads/Packages/com.unity.asset-store-tools/Editor/Previews/Scripts/Generators/Custom/TypeGenerators/TypePreviewGeneratorFromScene.cs:29

namespace AssetStoreTools.Previews.Generators.Custom.TypeGenerators
{
    internal abstract class TypePreviewGeneratorFromScene : TypePreviewGeneratorBase
    {
        protected new TypePreviewGeneratorFromSceneSettings Settings;

        private CancellationTokenSource _cancellationTokenSource;

        public TypePreviewGeneratorFromScene(TypePreviewGeneratorFromSceneSettings settings) : base(settings)
        {
            Settings = settings;
        }

        public override void ValidateSettings()
        {
            base.ValidateSettings();

            if (Settings.Screenshotter == null)
                throw new ArgumentException("Screenshotter cannot be null");
        }

        protected sealed override async Task<List<PreviewMetadata>> GenerateImpl(IEnumerable<UnityEngine.Object> assets)
        {
            var originalScenePath = EditorSceneManager.GetActiveScene().path;
            await PreviewSceneUtility.OpenPreviewSceneForCurrentPipeline();

            try
            {
                _cancellationTokenSource = new CancellationTokenSource();
                EditorSceneManager.sceneOpened += SceneOpenedDuringGeneration;
                return await GeneratePreviewsInScene(assets);
            }
            finally
            {
                EditorSceneManager.sceneOpened -= SceneOpenedDuringGeneration;
                _cancellationTokenSource.Dispose();
                if (!string.IsNullOrEmpty(originalScenePath))

View on GitHub (pinned to c21bf496bc)

Solutions

1. Create and assign a screenshotter instance (e.g., a SceneScreenshotter subclass) to Settings.Screenshotter before calling Generate.
2. Initialize the screenshotter in a settings factory method alongside dimension validation.
3. If deserializing settings, reconstruct the screenshotter programmatically after load.

Example fix

// before
var settings = new TypePreviewGeneratorFromSceneSettings { InputPaths = paths, OutputPath = outPath, Screenshotter = null };
var generator = new TypePreviewGeneratorFromScene(settings);
await generator.Generate();

// after
var screenshotter = new SceneScreenshotter(screenshotSettings);
var settings = new TypePreviewGeneratorFromSceneSettings { InputPaths = paths, OutputPath = outPath, Screenshotter = screenshotter };
var generator = new TypePreviewGeneratorFromScene(settings);
await generator.Generate();

if (settings.Screenshotter == null)
    settings.Screenshotter = new SceneScreenshotter(CreateDefaultScreenshotSettings());
// or validate:
if (settings.Screenshotter == null)
    throw new InvalidOperationException("A Screenshotter instance must be assigned before generation.");

static bool HasValidScreenshotter(TypePreviewGeneratorFromSceneSettings s)
    => s?.Screenshotter != null;

try
{
    await generator.Generate();
}
catch (ArgumentException ex) when (ex.Message.Contains("Screenshotter cannot be null"))
{
    settings.Screenshotter = new SceneScreenshotter(CreateDefaultScreenshotSettings());
    await generator.Generate();
}

When it happens

Trigger: Calling Generate() or ValidateSettings() on a TypePreviewGeneratorFromScene with Settings.Screenshotter == null. The screenshotter is used in GeneratePreviewsInScene to capture each object.

Common situations: Settings constructed without assigning a Screenshotter; screenshotter field was cleared during settings reset; deserialized settings where the screenshotter (a non-serializable object reference) was not reconnected; UI didn't create the screenshotter before starting generation.

Related errors

• Width should be larger than 0
• Height should be larger than 0
• Depth should be larger than 0
• Native width should be larger than 0
• Native height should be larger than 0

AI-assisted analysis of CoplayDev/unity-mcp@c21bf496bc (2026-08-13). Data as JSON: /api/errors/23d1731c4168d8de. Report an issue: GitHub.