microsoft/semantic-kernel · error · ArgumentNullException

runtimeClient

Error message

runtimeClient

What it means

This is a constructor guard on BedrockAgentThread. The thread requires an IAmazonBedrockAgentRuntime client to create, delete, and interact with sessions, so a null client would cause NullReferenceException later during any operation. The check fails fast with the parameter name 'runtimeClient' so the caller knows exactly which argument was null.

Solutions

1. Construct the client before the thread: `new AmazonBedrockAgentRuntimeClient(credentials, region)` and pass the non-null instance.
2. If using DI, register the AWS service: `services.AddAWSService<IAmazonBedrockAgentRuntime>()` and inject it into the component that creates the thread.
3. Add a null-check in your own factory/build method so the thread is never constructed with a null client.

Example fix

// before
var thread = new BedrockAgentThread(runtimeClient: null, sessionId);

// after
var client = new AmazonBedrockAgentRuntimeClient(awsCredentials, RegionEndpoint.USEast1);
var thread = new BedrockAgentThread(client, sessionId);

IAmazonBedrockAgentRuntime? runtimeClient = ResolveClient();
if (runtimeClient is null)
    throw new InvalidOperationException("Bedrock runtime client could not be resolved; check DI/AWS config.");
var thread = new BedrockAgentThread(runtimeClient, sessionId);

static bool IsValidBedrockRuntimeClient(IAmazonBedrockAgentRuntime? c) => c is not null;

try { var thread = new BedrockAgentThread(client, sessionId); }
catch (ArgumentNullException ex) when (ex.ParamName == "runtimeClient")
{
    logger.LogError("Bedrock runtime client was null. Register AddAWSService<IAmazonBedrockAgentRuntime>().");
    throw;
}

When it happens

Trigger: Instantiating `new BedrockAgentThread(null)` or `new BedrockAgentThread(runtimeClient: null, sessionId)`. Passing a DI-resolved client that resolved to null because the AWS service registration was missing or misconfigured.

Common situations: Forgot to register `AddAWSService<IAmazonBedrockAgentRuntime>()` in the DI container; the client field was never assigned before thread construction; a factory method returned null under an error path.

Related errors

• client
• Agent did not reach status
• Failed to handle Bedrock Agent stream event.
• Failed to handle Bedrock Agent stream event
• Failed to invoke agent. Status code

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/3607ef806be11d2d. Report an issue: GitHub.

Appendix: source

Thrown at dotnet/src/Agents/Bedrock/BedrockAgentThread.cs:24

using Amazon.BedrockAgentRuntime;

namespace Microsoft.SemanticKernel.Agents.Bedrock;
/// <summary>
/// Represents a conversation thread for a Bedrock agent.
/// </summary>
public sealed class BedrockAgentThread : AgentThread
{
    private readonly IAmazonBedrockAgentRuntime _runtimeClient;

    /// <summary>
    /// Initializes a new instance of the <see cref="BedrockAgentThread"/> class.
    /// </summary>
    /// <param name="runtimeClient">A client used to interact with the Bedrock Agent runtime service.</param>
    /// <param name="sessionId">An optional session Id to continue an existing session.</param>
    /// <exception cref="ArgumentNullException"></exception>
    public BedrockAgentThread(IAmazonBedrockAgentRuntime runtimeClient, string? sessionId = null)
    {
        this._runtimeClient = runtimeClient ?? throw new ArgumentNullException(nameof(runtimeClient));
        this.Id = sessionId;
    }

    /// <summary>
    /// Creates the thread and returns the thread id.
    /// </summary>
    /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
    /// <returns>A task that completes when the thread has been created.</returns>
    public new Task CreateAsync(CancellationToken cancellationToken = default)
    {
        return base.CreateAsync(cancellationToken);
    }

    /// <inheritdoc />
    protected override async Task<string?> CreateInternalAsync(CancellationToken cancellationToken)
    {
        const string ErrorMessage = "The thread could not be created due to an error response from the service.";

View on GitHub (pinned to c028a0c7dc)