SixLabors/ImageSharp · error · NotSupportedException

Newly created value for tag

Error message

Newly created value for tag {tag} is null.

What it means

ExifProfile.SetValueInternal could not create a new ExifValue for the requested EXIF tag: ExifValues.Create(tag) returned null, meaning the tag has no known type metadata in ImageSharp's EXIF tables, so a NotSupportedException is thrown rather than silently adding an unusable value.

Solutions

  1. Only set values for tags ImageSharp supports; check support by ensuring ExifValues.Create-equivalent lookup succeeds, or first read the profile to see which tags exist.
  2. For custom tags, add the value to the profile at the raw-data level or via a supported generic tag type instead of SetValue.
  3. Upgrade ImageSharp — newer versions extend the supported EXIF tag table.

Example fix

// before
profile.SetValue((ExifTagValue)0x9C9B, "MyData"); // unsupported custom tag -> throws
// after
if (profile.TryGetValue((ExifTagValue)0x9C9B, out _))
{
    profile.SetValue((ExifTagValue)0x9C9B, "MyData");
}
else
{
    // handle unsupported tag: skip or store elsewhere
}
Defensive patterns

Strategy: try-catch

Validate before calling

// Only call SetValue for tags the profile already exposes or that are known-supported
bool tagWritable(ExifProfile profile, ExifTagValue tag) =>
    profile.TryGetValue(tag, out _) || Enum.IsDefined(typeof(ExifTagValue), tag); // plus known-supported check

Try / catch

try { profile.SetValue(tag, value); }
catch (NotSupportedException ex)
{ /* unsupported tag: skip, log, or persist metadata by other means */ }

Prevention

When it happens

Trigger: Calling ExifProfile.SetValue(tag, value) with a tag not present in the profile and not in ExifValues' supported tag table — e.g. custom/manufacturer-specific tags or a numeric (ExifTagValue) tag with no registered ExifValue factory.

Common situations: Writing maker-note or non-standard EXIF tags that ImageSharp doesn't model; typos in tag constants; trying to write tags added in newer EXIF specs than the library supports.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of SixLabors/ImageSharp@59ce6af6fc (2026-09-13). Data as JSON: /api/errors/df91c72a9291efa0. Report an issue: GitHub.

Appendix: source

Thrown at src/ImageSharp/Metadata/Profiles/Exif/ExifProfile.cs:288

    /// <summary>
    /// Sets the value of the specified tag.
    /// </summary>
    /// <param name="tag">The tag of the Exif value.</param>
    /// <param name="value">The value.</param>
    /// <exception cref="NotSupportedException">The newly created value is null.</exception>
    internal void SetValueInternal(ExifTag tag, object? value)
    {
        foreach (IExifValue exifValue in this.Values)
        {
            if (exifValue.Tag == tag)
            {
                exifValue.TrySetValue(value);
                return;
            }
        }

        ExifValue? newExifValue = ExifValues.Create(tag) ?? throw new NotSupportedException($"Newly created value for tag {tag} is null.");

        newExifValue.TrySetValue(value);
        this.values.Add(newExifValue);
    }

    /// <summary>
    /// Synchronizes the profiles with the specified metadata.
    /// </summary>
    /// <param name="metadata">The metadata.</param>
    internal void Sync(ImageMetadata metadata)
    {
        this.SyncResolution(ExifTag.XResolution, metadata.HorizontalResolution);
        this.SyncResolution(ExifTag.YResolution, metadata.VerticalResolution);
    }

    internal void SyncDimensions(int width, int height)
    {
        if (this.TryGetValue(ExifTag.PixelXDimension, out _))

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