microsoft/semantic-kernel · error · InvalidOperationException

Image content MimeType is empty.

Error message

Image content MimeType is empty.

What it means

Thrown by GeminiRequest.GetMimeTypeFromImageContent when ImageContent.MimeType is null. The Gemini API requires a MIME type for both inline data (InlineDataPart.MimeType) and file data (FileDataPart.MimeType) parts. Without a MIME type, the model cannot determine the media format of the image.

Source

Thrown at dotnet/src/Connectors/Connectors.Google/Core/Gemini/Models/GeminiRequest.cs:319

        if (imageContent.Uri is not null)
        {
            return new GeminiPart
            {
                FileData = new GeminiPart.FileDataPart
                {
                    MimeType = GetMimeTypeFromImageContent(imageContent),
                    FileUri = imageContent.Uri ?? throw new InvalidOperationException("Image content URI is empty.")
                }
            };
        }

        throw new InvalidOperationException("Image content does not contain any data or uri.");
    }

    private static string GetMimeTypeFromImageContent(ImageContent imageContent)
    {
        return imageContent.MimeType
               ?? throw new InvalidOperationException("Image content MimeType is empty.");
    }

    /// <summary>
    /// Creates a GeminiPart with FunctionResponse containing multimodal image data (Gemini 3+ only).
    /// </summary>
    private static GeminiPart CreateImageFunctionResponsePart(string functionName, ImageContent imageContent)
    {
        if (imageContent.Data is not { IsEmpty: false })
        {
            throw new InvalidOperationException("ImageContent in function result must contain binary data.");
        }

        return new GeminiPart
        {
            FunctionResponse = new GeminiPart.FunctionResponsePart
            {
                FunctionName = functionName,
                Response = new(s_imageFunctionResponseEnvelope),

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Always set MimeType when constructing ImageContent: new ImageContent(data) { MimeType = "image/png" } or new ImageContent(uri) { MimeType = "image/jpeg" }.
2. Infer the MIME type from the file extension if not explicitly available: var mime = Path.GetExtension(path).ToLowerInvariant() switch { ".png" => "image/png", ".jpg" or ".jpeg" => "image/jpeg", _ => "application/octet-stream" };
3. Validate before the call: if (string.IsNullOrEmpty(image.MimeType)) throw new InvalidOperationException("MimeType required for Gemini.");

Example fix

// before — no MIME type
var content = new ImageContent(await File.ReadAllBytesAsync("photo.jpg"));

// after — include MIME type
var content = new ImageContent(await File.ReadAllBytesAsync("photo.jpg"))
{
    MimeType = "image/jpeg"
};

static void ValidateImageMimeType(ImageContent image)
{
    if (string.IsNullOrWhiteSpace(image.MimeType))
        throw new ArgumentException(
            "ImageContent.MimeType is required for Gemini. " +
            "Set it explicitly (e.g. 'image/png', 'image/jpeg').");
}

static bool HasMimeType(ImageContent img) =>
    !string.IsNullOrWhiteSpace(img.MimeType);

try { await client.GetChatMessageContentsAsync(history, settings, ct); }
catch (InvalidOperationException ex) when (ex.Message.Contains("MimeType is empty"))
{
    // Infer from file extension if available and retry
    var mimeType = InferMimeType(imageUri);
    imageContent.MimeType = mimeType;
    await client.GetChatMessageContentsAsync(history, settings, ct);
}

When it happens

Trigger: Constructing an ImageContent with data or a URI but without setting the MimeType property. The method is called from CreateGeminiPartFromImage in both the inline-data path and the file-data path, so it fires whenever either path needs a MIME type and none is set.

Common situations: Loading raw bytes from a source that does not expose content type (e.g. a byte array from memory). Using new ImageContent(bytes) without the mimeType parameter. Deserializing an ImageContent from a message where the content-type header was stripped. Passing a URI from a CDN where the extension is ambiguous.

Related errors

• Image content does not contain any data or uri.
• ImageContent in function result must contain binary data.
• MaxTokens {maxTokens} is not valid, the value must be greate
• Chat history can't contain only system messages.
• Auto-invocation of tool calls may only be used with a {nameo

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/120a27cd3dc729da. Report an issue: GitHub.