dotnet/orleans · error · ArgumentNullException

Value cannot be null. (Parameter 'createClient')

Error message

Value cannot be null. (Parameter 'createClient')

What it means

Thrown by CosmosOptions.ConfigureCosmosClient when the supplied client-factory delegate is null. The Cosmos provider needs a non-null factory to lazily construct the CosmosClient.

Source

Thrown at src/Azure/Shared/Cosmos/CosmosOptions.cs:116

    /// <summary>
    /// Configures the Cosmos DB client.
    /// </summary>
    /// <param name="accountEndpoint">The account endpoint. In the form of <code>https://{databaseaccount}.documents.azure.com:443/</code>, <see href="https://learn.microsoft.com/rest/api/cosmos-db/cosmosdb-resource-uri-syntax-for-rest"/></param>
    /// <param name="authKeyOrResourceToken">The Cosmos account key or resource token to use to create the client.</param>
    /// <see cref="CosmosClient(string, TokenCredential, CosmosClientOptions)"/>
    public void ConfigureCosmosClient(string accountEndpoint, string authKeyOrResourceToken)
    {
        CreateClient = _ => new(new CosmosClient(accountEndpoint, authKeyOrResourceToken, ClientOptions));
    }

    /// <summary>
    /// Configures the Cosmos DB client.
    /// </summary>
    /// <param name="createClient">The delegate used to create the Cosmos DB client.</param>
    public void ConfigureCosmosClient(Func<IServiceProvider, ValueTask<CosmosClient>> createClient)
    {
        CreateClient = createClient ?? throw new ArgumentNullException(nameof(createClient));
    }

    /// <summary>
    /// Factory method for creating a <see cref="CosmosClient"/>.
    /// </summary>
    internal Func<IServiceProvider, ValueTask<CosmosClient>> CreateClient { get; private set; } = null!;
}

/// <summary>
/// Functionality for executing operations using the Cosmos DB client.
/// </summary>
public interface ICosmosOperationExecutor
{
    /// <summary>
    /// Executes the provided Cosmos DB operation.
    /// </summary>
    /// <typeparam name="TArg">The function argument.</typeparam>
    /// <typeparam name="TResult">The result value.</typeparam>

View on GitHub (pinned to fca799fa70)

Solutions

1. Pass a non-null Func<IServiceProvider, ValueTask<CosmosClient>>, e.g. _ => new(new CosmosClient(endpoint, key, options)).
2. If you only have an endpoint and key, call ConfigureCosmosClient(string accountEndpoint, string authKeyOrResourceToken) instead.
3. Register the factory in DI and resolve it before calling ConfigureCosmosClient.

Example fix

// before
options.ConfigureCosmosClient(null);

// after
options.ConfigureCosmosClient(_ => new(new CosmosClient(endpoint, key, options.ClientOptions)));

if (createClient is null) throw new ArgumentNullException(nameof(createClient));
options.ConfigureCosmosClient(createClient);

static bool IsValidFactory(Func<IServiceProvider, ValueTask<CosmosClient>>? f) => f is not null;

When it happens

Trigger: Calling ConfigureCosmosClient(null) or passing a delegate resolved from a nullable DI service that was never registered.

Common situations: Refactor that drops the factory assignment; conditional configuration branch that leaves the delegate null; copy-paste from a sample that omits the lambda.

Related errors

• credential
• connection
• createConnection
• Configuration for Azure Cosmos DB provider {_name} is invali
• Configuration for Azure Cosmos DB provider {_name} is invali

AI-assisted analysis of dotnet/orleans@fca799fa70 (2026-08-13). Data as JSON: /api/errors/28543a8e9751c73e. Report an issue: GitHub.