microsoft/semantic-kernel · error · KernelException

Unable to create gRPC request message for the '{operation.Na

Error message

Unable to create gRPC request message for the '{operation.Name}' gRPC operation.

What it means

Thrown when `JsonSerializer.Deserialize(payload, type, ...)` returns null while building the gRPC request message. A null result means the JSON payload was valid JSON (`null` literal) or deserialized to a null reference of the contract type, so the runtime cannot proceed.

Source

Thrown at dotnet/src/Functions/Functions.Grpc/GrpcOperationRunner.cs:266

    /// <summary>
    /// Creates a gRPC operation request.
    /// </summary>
    /// <param name="operation">The gRPC operation.</param>
    /// <param name="type">The operation request data type.</param>
    /// <param name="arguments">The operation arguments.</param>
    /// <returns>The operation request instance.</returns>
    private object GenerateOperationRequest(GrpcOperation operation, Type type, Dictionary<string, string> arguments)
    {
        //Getting 'payload' argument to by used as gRPC request message
        if (!arguments.TryGetValue(GrpcOperation.PayloadArgumentName, out string? payload) ||
            string.IsNullOrEmpty(payload))
        {
            throw new KernelException($"No '{GrpcOperation.PayloadArgumentName}' argument representing gRPC request message is found for the '{operation.Name}' gRPC operation.");
        }

        //Deserializing JSON payload to gRPC request message
        return JsonSerializer.Deserialize(payload!, type, s_propertyCaseInsensitiveOptions) ??
            throw new KernelException($"Unable to create gRPC request message for the '{operation.Name}' gRPC operation.");
    }

    /// <summary>
    /// Builds gRPC operation data contract type.
    /// </summary>
    /// <param name="dataContractMetadata">The data contract type metadata.</param>
    /// <returns>.NET type representing the data contract type.</returns>
    private static TypeInfo BuildGrpcOperationDataContractType(GrpcOperationDataContractType dataContractMetadata)
    {
        var assemblyName = new AssemblyName($"{dataContractMetadata.Name}Assembly");

        var assemblyBuilder = AssemblyBuilder.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run);

        var moduleBuilder = assemblyBuilder.DefineDynamicModule($"{dataContractMetadata.Name}Module");

        var typeBuilder = moduleBuilder.DefineType(dataContractMetadata.Name, TypeAttributes.Public | TypeAttributes.Sealed | TypeAttributes.Class);

        //Creating and adding a .NET property for each data contract filed

View on GitHub (pinned to c028a0c7dc)

Solutions

Ensure the payload is a non-null JSON object matching the operation's request contract.
Validate the payload is not literally `null` before invoking.
Log/inspect the payload string to confirm it carries the expected fields.

Example fix

// before
arguments["payload"] = "null";
// after
arguments["payload"] = "{\"id\":42,\"name\":\"x\"}";

Defensive patterns

Strategy: validation

Validate before calling

var p = arguments["payload"]?.ToString();
if (string.IsNullOrWhiteSpace(p) || p.Trim() == "null")
    throw new InvalidOperationException("payload must be a non-null JSON object");

Prevention

Serialize the request object rather than passing literal `null`.
Validate the payload JSON shape against the contract before invoking.

When it happens

Trigger: Passing `payload = "null"`; a payload that deserializes to a nullable/null default for the dynamically built contract type.

Common situations: Upstream serializer emitted `null`; payload built from a nullable reference that was null; contract type mismatch causing a null instance.

Related errors

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/977000811eb9d6d4. Report an issue: GitHub.