SignalR/SignalR · error · ArgumentNullException

connection

Error message

connection

What it means

Thrown by ConnectionExtensions.Send(IConnection, string connectionId, object value) when the connection argument is null. The extension method builds a ConnectionMessage and calls connection.Send, so a null connection cannot perform the broadcast.

Source

Thrown at src/Microsoft.AspNet.SignalR.Core/ConnectionExtensions.cs:26

using Microsoft.AspNet.SignalR.Infrastructure;

namespace Microsoft.AspNet.SignalR
{
    public static class ConnectionExtensions
    {
        /// <summary>
        /// Sends a message to all connections subscribed to the specified signal. An example of signal may be a
        /// specific connection id.
        /// </summary>
        /// <param name="connection">The connection</param>
        /// <param name="connectionId">The connectionId to send to.</param>
        /// <param name="value">The value to publish.</param>
        /// <returns>A task that represents when the broadcast is complete.</returns>
        public static Task Send(this IConnection connection, string connectionId, object value)
        {
            if (connection == null)
            {
                throw new ArgumentNullException("connection");
            }

            if (String.IsNullOrEmpty(connectionId))
            {
                throw new ArgumentException(Resources.Error_ArgumentNullOrEmpty, "connectionId");
            }

            var message = new ConnectionMessage(PrefixHelper.GetConnectionId(connectionId),
                                                value);

            return connection.Send(message);
        }

        /// <summary>
        /// Sends a message to all connections subscribed to the specified signal. An example of signal may be a
        /// specific connection id.
        /// </summary>
        /// <param name="connection">The connection</param>

View on GitHub (pinned to 693053b89a)

Solutions

1. Resolve the IConnection from GlobalHost.ConnectionManager.GetConnectionContext (or the resolver) before calling Send.
2. Guard the connection reference for null before invoking the extension.
3. Avoid calling Send after the application has shut down the connection.

Example fix

// before
var conn = (IConnection)null;
conn.Send(targetId, payload);

// after
var conn = GlobalHost.ConnectionManager.GetConnection<MyPersistentConnection>().Connection;
conn.Send(targetId, payload);

var connection = GlobalHost.ConnectionManager.GetConnection<MyPersistentConnection>().Connection;
if (connection != null)
    connection.Send(connectionId, value);

if (connection is IConnection c && c != null) { c.Send(connectionId, value); }

When it happens

Trigger: Calling connection.Send(connectionId, value) as an extension method on a null IConnection reference.

Common situations: Static helper usage where the IConnection was never resolved from the dependency resolver, or was nulled during shutdown.

Related errors

• connectionIds
• Argument cannot be null or empty
• connection
• request
• hubIncomingInvokerContext

AI-assisted analysis of SignalR/SignalR@693053b89a (2026-08-13). Data as JSON: /api/errors/ff8b71cba97dcb97. Report an issue: GitHub.