SignalR/SignalR · error · ArgumentNullException

connectionString

Error message

connectionString

What it means

ArgumentNullException guard in the StackExchangeRedis RedisScaleoutConfiguration constructor: connectionString must not be null. Note this checks only null (not empty) — an empty string is permitted and simply skips ConfigurationOptions parsing and Database detection.

Source

Thrown at src/Microsoft.AspNet.SignalR.StackExchangeRedis/RedisScaleoutConfiguration.cs:25

using StackExchange.Redis;

namespace Microsoft.AspNet.SignalR
{
    /// <summary>
    /// Settings for the Redis scale-out message bus implementation.
    /// </summary>
    public class RedisScaleoutConfiguration : ScaleoutConfiguration
    {
        public RedisScaleoutConfiguration(string server, int port, string password, string eventKey)
            : this(CreateConnectionString(server, port, password), eventKey)
        {
        }

        public RedisScaleoutConfiguration(string connectionString, string eventKey)
        {
            if (connectionString == null)
            {
                throw new ArgumentNullException("connectionString");
            }

            if (eventKey == null)
            {
                throw new ArgumentNullException("eventKey");
            }

            ConnectionString = connectionString;
            if (connectionString.Length > 0)
            {
                var options = ConfigurationOptions.Parse(connectionString);
                Database = options.DefaultDatabase.GetValueOrDefault(0);
            }
            EventKey = eventKey;
        }

        /// <summary>
        /// The connection string that needs to be passed to ConnectionMultiplexer

View on GitHub (pinned to 693053b89a)

Solutions

1. Provide a non-null connection string of the form 'host:port,password=...,abortConnect=false'.
2. If loading from config, verify the setting exists; treat missing as a startup error.
3. Prefer the (server, port, password, eventKey) overload which builds the string for you.

Example fix

// before
var cs = ConfigurationManager.AppSettings["RedisConn"];
var config = new RedisScaleoutConfiguration(cs, "SignalR"); // cs null -> throw

// after
var config = new RedisScaleoutConfiguration("redis.example.com", 6379, "password", "SignalR");
// or guard:
var cs = ConfigurationManager.AppSettings["RedisConn"] ?? throw new ConfigurationErrorsException("RedisConn missing");
var config = new RedisScaleoutConfiguration(cs, "SignalR");

if (connectionString == null) throw new ArgumentNullException(nameof(connectionString));
var config = new RedisScaleoutConfiguration(connectionString, eventKey);

When it happens

Trigger: new RedisScaleoutConfiguration(null, eventKey) is constructed (or the server/port/password overload builds a null string), hitting the guard at RedisScaleoutConfiguration.cs:25.

Common situations: The connection string is sourced from a missing config key and is null; a variable that was never assigned is passed; the 4-argument overload is fed a null server. Note: CreateConnectionString formats with string.Format so a null server would not itself trigger this guard (it produces "...password=...") — the null check specifically catches a null connectionString argument to the 2-arg constructor.

Related errors

• configuration
• eventKey
• connectionString
• messages
• configuration

AI-assisted analysis of SignalR/SignalR@693053b89a (2026-08-13). Data as JSON: /api/errors/4c0c976009b9f30e. Report an issue: GitHub.