SixLabors/ImageSharp · error · ArgumentException

Must not be empty.

Error message

Must not be empty.

What it means

The ImageFrameCollection<TPixel> constructor requires at least one frame because an Image must always contain at least one frame. Passing an empty enumerable of frames violates this invariant and throws ArgumentException. A zero-frame image is not a valid state in ImageSharp.

Solutions

1. Ensure at least one ImageFrame<TPixel> is created and added before constructing the collection.
2. Guard the frames list: if it is empty after assembly, create a default frame instead of passing an empty list.
3. Check the upstream logic that produced the frames collection for accidental emptying.

Example fix

// before
var frames = filteredFrames; // may be empty
var collection = new ImageFrameCollection<Rgba32>(image, frames);
// after
if (frames.Count == 0)
{
    frames.Add(new ImageFrame<Rgba32>(configuration, width, height));
}
var collection = new ImageFrameCollection<Rgba32>(image, frames);

if (frames is null || frames.Count == 0) throw new ArgumentException("At least one frame is required.", nameof(frames));

static bool HasFrames(IReadOnlyCollection<ImageFrame<TPixel>> frames) => frames is { Count: > 0 };

try { var collection = new ImageFrameCollection<Rgba32>(image, frames); }
catch (ArgumentException ex) { /* supply a default frame and retry */ }

When it happens

Trigger: Constructing ImageFrameCollection<TPixel> (typically via Image load paths or constructor overloads) with an empty IEnumerable<ImageFrame<TPixel>>.

Common situations: Building an image programmatically by assembling frames into a list that ended up empty (e.g. a filtering step removed all frames), or calling a low-level constructor directly with a collection built conditionally.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• Cannot detect image format from empty data.
• Cannot remove last frame.
• No encoder was found for extension
• No encoder was found for extension
• The ANI file contains an unsupported frame format.

AI-assisted analysis of SixLabors/ImageSharp@59ce6af6fc (2026-09-13). Data as JSON: /api/errors/81e51e27085c2376. Report an issue: GitHub.

Appendix: source

Thrown at src/ImageSharp/ImageFrameCollection{TPixel}.cs:59

    internal ImageFrameCollection(Image<TPixel> parent, IEnumerable<ImageFrame<TPixel>> frames)
    {
        Guard.NotNull(parent, nameof(parent));
        Guard.NotNull(frames, nameof(frames));

        this.parent = parent;

        // Frames are already cloned by the caller
        foreach (ImageFrame<TPixel> f in frames)
        {
            this.ValidateFrame(f);
            this.frames.Add(f);
        }

        // Ensure at least 1 frame was added to the frames collection
        if (this.frames.Count == 0)
        {
            throw new ArgumentException("Must not be empty.", nameof(frames));
        }
    }

    /// <summary>
    /// Gets the number of frames.
    /// </summary>
    public override int Count => this.frames.Count;

    /// <summary>
    /// Gets the root frame.
    /// </summary>
    public new ImageFrame<TPixel> RootFrame
    {
        get
        {
            this.EnsureNotDisposed();

            // frame collection would always contain at least 1 frame

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