microsoft/autogen · error · ArgumentException

Content is null and metadata is null

Error message

Content is null and metadata is null

What it means

MessageExtension's user-message conversion throws ArgumentException when a message has neither usable content nor recognized metadata. It first tries to build multi-modal items from metadata (e.g. image URLs under the image content-type key); if no items were produced and the Content is null/empty, nothing can be sent to the API.

Source

Thrown at dotnet/src/AutoGen.OpenAI.V1/Extension/MessageExtension.cs:44

            foreach (var item in message.Metadata)
            {
                if (item.Key == TEXT_CONTENT_TYPE && item.Value is string txt)
                {
                    itemList.Add(new ChatMessageTextContentItem(txt));
                }
                else if (item.Key == IMAGE_CONTENT_TYPE && item.Value is string url)
                {
                    itemList.Add(new ChatMessageImageContentItem(new Uri(url)));
                }
            }

            if (itemList.Count > 0)
            {
                return new ChatRequestUserMessage(itemList);
            }
            else
            {
                throw new ArgumentException("Content is null and metadata is null");
            }
        }
        else if (!string.IsNullOrEmpty(message?.Content))
        {
            return new ChatRequestUserMessage(message!.Content);
        }

        throw new ArgumentException("Content is null and metadata is null");
    }

    [Obsolete("This method is deprecated")]
    public static IEnumerable<ChatRequestMessage> ToOpenAIChatRequestMessage(this IAgent agent, IMessage message)
    {
        if (message is IMessage<ChatRequestMessage> oaiMessage)
        {
            // short-circuit
            return [oaiMessage.Content];
        }

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Ensure the message has non-empty Content before sending
2. For image-only messages, set Metadata[IMAGE_CONTENT_TYPE] = imageUrl (string) so the multi-modal branch produces a content item
3. Filter out empty messages from conversation history before conversion

Example fix

// before
var msg = new TextMessage(Role.User, content: null);
await agent.SendAsync(msg);

// after
var msg = new TextMessage(Role.User, "Describe this image")
{
    Metadata = new Dictionary<string, object> { [IMAGE_CONTENT_TYPE] = imageUrl }
};
await agent.SendAsync(msg);

bool IsSendable(IMessage m) =>
    !string.IsNullOrEmpty(m.GetContent()) ||
    m.Metadata?.Any(kv => kv.Key == IMAGE_CONTENT_TYPE && kv.Value is string) == true;

catch (ArgumentException ex) when (ex.Message == "Content is null and metadata is null")
{
    logger.LogWarning("Dropped empty message");
}

When it happens

Trigger: Calling the conversion with a TextMessage whose Content is null/empty and whose Metadata lacks IMAGE_CONTENT_TYPE entries, or an IMessage with null Content and null/empty Metadata.

Common situations: Passing placeholder or uninitialized messages into the connector; streaming partial updates where content hasn't arrived yet; metadata keys set with non-string values so the image branch is skipped.

Related errors

• Content is null
• Unknown message type: {m.GetType()}
• Unknown message type: {message.GetType()}
• Failed to fetch galleries
• Failed to fetch gallery

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/11d1d5aae12d916f. Report an issue: GitHub.