dotnet/reactive · error · ArgumentNullException

Value cannot be null. (Parameter 'optimizationInterfaces')

Error message

Value cannot be null. (Parameter 'optimizationInterfaces')

What it means

The same DisableOptimizations overload also validates the optimizationInterfaces parameter; passing a null Type[] throws ArgumentNullException naming 'optimizationInterfaces'. The wrapper needs the array (possibly empty) to know which optimizations to suppress.

Solutions

1. Pass an empty array instead of null when no optimizations should be disabled
2. Ensure the code building the Type[] returns Array.Empty<Type>() rather than null
3. Check the variable for null before the call

Example fix

// before
Type[] ifs = GetDisabledOptimizations(); // returns null
var s = scheduler.DisableOptimizations(ifs);
// after
var ifs = GetDisabledOptimizations() ?? Array.Empty<Type>();
var s = scheduler.DisableOptimizations(ifs);

optimizationInterfaces ??= Array.Empty<Type>();

static bool HasInterfaceList(Type[] t) => t != null;

try { wrapped = scheduler.DisableOptimizations(list); }
catch (ArgumentNullException) { wrapped = scheduler.DisableOptimizations(Array.Empty<Type>()); }

When it happens

Trigger: Calling scheduler.DisableOptimizations((Type[])null) or passing a variable typed Type[] that is null, typically built by a method that returned null instead of an empty array.

Common situations: Building the list of optimization interfaces dynamically; configuration-driven type lists that were never populated; API returning null for 'no restrictions'.

Related errors

• action (Parameter 'action')
• action (Parameter 'action')
• action (Parameter 'action')
• action (Parameter 'action')
• action (Parameter 'action')

AI-assisted analysis of dotnet/reactive@94b5d5ab91 (2026-09-15). Data as JSON: /api/errors/392725565330c6c4. Report an issue: GitHub.

Appendix: source

Thrown at Rx.NET/Source/src/System.Reactive/Concurrency/Scheduler.Wrappers.cs:41

        }

        /// <summary>
        /// Returns a scheduler that represents the original scheduler, without the specified set of interface-based optimizations (e.g. long running scheduling).
        /// </summary>
        /// <param name="scheduler">Scheduler to disable the specified optimizations for.</param>
        /// <param name="optimizationInterfaces">Types of the optimization interfaces that have to be disabled.</param>
        /// <returns>Proxy to the original scheduler but without the specified optimizations enabled.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="scheduler"/> or <paramref name="optimizationInterfaces"/> is <c>null</c>.</exception>
        public static IScheduler DisableOptimizations(this IScheduler scheduler, params Type[] optimizationInterfaces)
        {
            if (scheduler == null)
            {
                throw new ArgumentNullException(nameof(scheduler));
            }

            if (optimizationInterfaces == null)
            {
                throw new ArgumentNullException(nameof(optimizationInterfaces));
            }

            return new DisableOptimizationsScheduler(scheduler, optimizationInterfaces);
        }

        /// <summary>
        /// Returns a scheduler that wraps the original scheduler, adding exception handling for scheduled actions.
        /// </summary>
        /// <typeparam name="TException">Type of the exception to check for.</typeparam>
        /// <param name="scheduler">Scheduler to apply an exception filter for.</param>
        /// <param name="handler">Handler that's run if an exception is caught. The exception will be rethrown if the handler returns false.</param>
        /// <returns>Wrapper around the original scheduler, enforcing exception handling.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="scheduler"/> or <paramref name="handler"/> is <c>null</c>.</exception>
        public static IScheduler Catch<TException>(this IScheduler scheduler, Func<TException, bool> handler)
            where TException : Exception
        {
            if (scheduler == null)
            {

View on GitHub (pinned to 94b5d5ab91)