CoplayDev/unity-mcp · error · ArgumentException

Output path cannot be null

Error message

Output path cannot be null

What it means

Thrown by PreviewGeneratorBase.Validate() (PreviewGeneratorBase.cs:40) when Settings.OutputPath is null or empty. OutputPath is where preview files are written (Directory.CreateDirectory and file writes use it). Null/empty would make file IO fail. Base check, runs for all generators before GenerateImpl(), outside its try/catch — an uncaught ArgumentException.

Source

Thrown at TestProjects/AssetStoreUploads/Packages/com.unity.asset-store-tools/Editor/Previews/Scripts/Generators/PreviewGeneratorBase.cs:40

        {
            Validate();

            var result = await GenerateImpl();
            if (result.Success)
            {
                CachingService.CacheMetadata(result.GeneratedPreviews);
            }

            return result;
        }

        protected virtual void Validate()
        {
            if (Settings.InputPaths == null || Settings.InputPaths.Length == 0)
                throw new ArgumentException("Input paths cannot be null");

            if (string.IsNullOrEmpty(Settings.OutputPath))
                throw new ArgumentException("Output path cannot be null");
        }

        protected abstract Task<PreviewGenerationResult> GenerateImpl();
    }
}

View on GitHub (pinned to c21bf496bc)

Solutions

1. Set Settings.OutputPath to a non-empty folder path before Generate().
2. Disable Generate in the UI until an output path is selected.
3. Assign OutputPath alongside InputPaths at construction.

Example fix

// before
var settings = new CustomPreviewGenerationSettings { InputPaths = paths /* OutputPath missing */ };
await new CustomPreviewGenerator(settings).Generate(); // throws

// after
var settings = new CustomPreviewGenerationSettings { InputPaths = paths, OutputPath = "Assets/Previews" };
await new CustomPreviewGenerator(settings).Generate();

if (string.IsNullOrEmpty(settings.OutputPath))
    throw new InvalidOperationException("PreviewGenerationSettings.OutputPath must be a non-empty path before generating.");

static bool HasOutputPath(PreviewGenerationSettings s) => s != null && !string.IsNullOrEmpty(s.OutputPath);

try { await generator.Generate(); }
catch (ArgumentException ex) when (ex.Message.Contains("Output path")) { /* report missing output path */ }

When it happens

Trigger: Calling Generate() with OutputPath unset (null) or set to an empty string. Occurs when settings are built without OutputPath, or when an output-folder picker returns empty.

Common situations: Settings initializer that sets InputPaths but not OutputPath; UI flow that allows Generate with no output folder chosen; a path that was cleared before submit.

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/b74369d666a68156. Report an issue: GitHub.