microsoft/autogen · error · ArgumentNullException

modelName is a required property for LMStudioConfig and cann

Error message

modelName is a required property for LMStudioConfig and cannot be null

What it means

Thrown by the LMStudioConfig(host, port, modelName) constructor when modelName is null. LMStudioConfig requires a model name because LM Studio serves a specific loaded model per request path; the guard fires before any property is set, using ArgumentNullException (with the message as the paramName argument).

Source

Thrown at dotnet/src/AutoGen/LMStudioConfig.cs:23

using System.ClientModel;
using OpenAI;
using OpenAI.Chat;

namespace AutoGen;

/// <summary>
/// Add support for consuming openai-like API from LM Studio
/// </summary>
public class LMStudioConfig : ILLMConfig
{
    public LMStudioConfig(string host, int port, string modelName)
    {
        this.Host = host;
        this.Port = port;
        this.Uri = new Uri($"http://{host}:{port}/v1");
        if (modelName == null)
        {
            throw new ArgumentNullException("modelName is a required property for LMStudioConfig and cannot be null");
        }
        this.ModelName = modelName;
    }

    public LMStudioConfig(Uri uri, string modelName)
    {
        this.Uri = uri;
        this.Host = uri.Host;
        this.Port = uri.Port;
        if (modelName == null)
        {
            throw new ArgumentNullException("modelName is a required property for LMStudioConfig and cannot be null");
        }
        this.ModelName = modelName;
    }

    public string Host { get; }

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Provide a non-null modelName matching the model loaded in LM Studio (see the 'model' field in LM Studio's list-models response)
2. Fix the configuration source so ModelName cannot resolve to null (required setting, startup validation)
3. Guard at the call site: if (modelName is null) log a clear error about the missing setting before constructing the config

Example fix

// before
var cfg = new LMStudioConfig("localhost", 1234, Environment.GetEnvironmentVariable("LM_MODEL")); // null if unset
// after
var model = Environment.GetEnvironmentVariable("LM_MODEL") ?? throw new InvalidOperationException("LM_MODEL is not set");
var cfg = new LMStudioConfig("localhost", 1234, model);

var modelName = config["LMStudio:ModelName"] as string;
if (string.IsNullOrWhiteSpace(modelName)) throw new InvalidOperationException("LMStudio:ModelName is required");
var cfg = new LMStudioConfig(host, port, modelName);

catch (ArgumentNullException ex) when (ex.Message.Contains("modelName")) { throw new ConfigurationException("LM Studio model name is missing; set it in configuration", ex); }

When it happens

Trigger: Calling new LMStudioConfig(host, port, null) or new LMStudioConfig(host, port, modelName) where modelName came from configuration/environment that was unset and resolved to null.

Common situations: Reading ModelName from appsettings/environment and forgetting it in one environment (staging/prod), so it deserializes as null; building configs from user input where the model field was left blank; JSON deserialization of a config object without a modelName key.

Related errors

• Value cannot be null. (Parameter 'array')
• The recent update is not a TextMessage
• The content has more than one choice. Please try another inp
• Invalid ChatResponseMessage
• Invalid message type: {m.GetType().Name}

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/b7b56148729e7707. Report an issue: GitHub.