dotnet/reactive · error · ArgumentNullException

Value cannot be null. (Parameter 'disposables')

Error message

Value cannot be null. (Parameter 'disposables')

What it means

The params-array overload StableCompositeDisposable.Create(params IDisposable[]) throws ArgumentNullException when the array itself is null. The array object (not its elements) must be non-null for the NAryArray composite to be built.

Solutions

1. Ensure the array is non-null before forwarding it to Create.
2. Pass an empty array instead of null when there are no disposables.
3. Filter the source collection and build the array defensively before calling Create.

Example fix

// before
var composite = StableCompositeDisposable.Create(collected); // collected is null
// after
var composite = StableCompositeDisposable.Create(collected ?? Array.Empty<IDisposable>());

if (disposables is null) disposables = Array.Empty<IDisposable>();
var composite = StableCompositeDisposable.Create(disposables);

static bool HasArray(IDisposable[] items) => items is not null;

try { var c = StableCompositeDisposable.Create(disposables); }
catch (ArgumentNullException ex) when (ex.ParamName == "disposables") { /* use empty composite */ }

When it happens

Trigger: Calling StableCompositeDisposable.Create(null) with a null IDisposable[] — typically passing a null array variable rather than relying on params expansion, or forwarding a null array from another API.

Common situations: Aggregating disposables collected in a list that was converted with ToArray() on a null source, or forwarding an optional params argument from a wrapper method.

Related errors

• Value cannot be null. (Parameter 'disposable1')
• Value cannot be null. (Parameter 'disposable2')
• Value cannot be null. (Parameter 'disposable')
• Value cannot be null. (Parameter 'disposable')
• RefCountDisposable

AI-assisted analysis of dotnet/reactive@94b5d5ab91 (2026-09-15). Data as JSON: /api/errors/3ca9898fea351bd2. Report an issue: GitHub.

Appendix: source

Thrown at Rx.NET/Source/src/System.Reactive/Disposables/StableCompositeDisposable.cs:46

            if (disposable2 == null)
            {
                throw new ArgumentNullException(nameof(disposable2));
            }

            return new Binary(disposable1, disposable2);
        }

        /// <summary>
        /// Creates a new group of disposable resources that are disposed together.
        /// </summary>
        /// <param name="disposables">Disposable resources to add to the group.</param>
        /// <returns>Group of disposable resources that are disposed together.</returns>
        public static ICancelable Create(params IDisposable[] disposables)
        {
            if (disposables == null)
            {
                throw new ArgumentNullException(nameof(disposables));
            }

            return new NAryArray(disposables);
        }

        /// <summary>
        /// Creates a group of disposable resources that are disposed together
        /// and without copying or checking for nulls inside the group.
        /// </summary>
        /// <param name="disposables">The array of disposables that is trusted
        /// to not contain nulls and gives no need to defensively copy it.</param>
        /// <returns>Group of disposable resources that are disposed together.</returns>
        internal static ICancelable CreateTrusted(params IDisposable[] disposables)
        {
            return new NAryTrustedArray(disposables);
        }

        /// <summary>

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