dotnet/reactive · error · ArgumentNullException

throw new ArgumentNullException(nameof(eleventh))

Error message

throw new ArgumentNullException(nameof(eleventh))

What it means

System.ArgumentNullException raised by the null-guard for the eleventh source in a CombineLatest overload in QbservableEx.Homoicon.cs. The overload validates all sources before calling Provider.CreateQuery so a null eleventh argument aborts composition.

Solutions

1. Pass a non-null eleventh IQbservable source.
2. Default missing optional streams to empty sequences.
3. Verify the DI registration or factory producing the eleventh stream.
4. Validate the whole source collection for nulls before composing.

Example fix

// before
CombineLatest(s1,...,s10, eleventh, sel); // eleventh == null
// after
var eleventh = eleventhSource ?? provider.CreateQuery<T11>(Expression.Constant(Observable.Empty<T11>()));
CombineLatest(s1,...,s10, eleventh, sel);

if (sources.Length < 11 || sources[10] == null) throw new ArgumentException("eleventh source missing");

static bool HasEleventh<T>(T[] sources) => sources.Length >= 11 && sources[10] != null;

try { CombineLatest(..., s11, ...); } catch (ArgumentNullException ex) when (ex.ParamName == "eleventh") { /* supply fallback and retry */ }

When it happens

Trigger: Invoking the 11+ argument Qbservable.CombineLatest overload with eleventh == null at line 916 of the guard chain.

Common situations: Optional feature stream not wired up; a dynamically generated source array containing a null at index 10.

Related errors

• fifth
• fourth
• third
• throw new ArgumentNullException(nameof(eighth))
• throw new ArgumentNullException(nameof(fifteenth))

AI-assisted analysis of dotnet/reactive@94b5d5ab91 (2026-09-15). Data as JSON: /api/errors/5819bda40d6d6709. Report an issue: GitHub.

Appendix: source

Thrown at Rx.NET/Source/src/System.Reactive/Linq/QbservableEx.Homoicon.cs:916

                throw new ArgumentNullException(nameof(second));
            if (third == null)
                throw new ArgumentNullException(nameof(third));
            if (fourth == null)
                throw new ArgumentNullException(nameof(fourth));
            if (fifth == null)
                throw new ArgumentNullException(nameof(fifth));
            if (sixth == null)
                throw new ArgumentNullException(nameof(sixth));
            if (seventh == null)
                throw new ArgumentNullException(nameof(seventh));
            if (eighth == null)
                throw new ArgumentNullException(nameof(eighth));
            if (ninth == null)
                throw new ArgumentNullException(nameof(ninth));
            if (tenth == null)
                throw new ArgumentNullException(nameof(tenth));
            if (eleventh == null)
                throw new ArgumentNullException(nameof(eleventh));
            if (twelfth == null)
                throw new ArgumentNullException(nameof(twelfth));
            if (thirteenth == null)
                throw new ArgumentNullException(nameof(thirteenth));
            if (fourteenth == null)
                throw new ArgumentNullException(nameof(fourteenth));
            if (fifteenth == null)
                throw new ArgumentNullException(nameof(fifteenth));
            if (sixteenth == null)
                throw new ArgumentNullException(nameof(sixteenth));

            return first.Provider.CreateQuery<(TFirst First, TSecond Second, TThird Third, TFourth Fourth, TFifth Fifth, TSixth Sixth, TSeventh Seventh, TEighth Eighth, TNinth Ninth, TTenth Tenth, TEleventh Eleventh, TTwelfth Twelfth, TThirteenth Thirteenth, TFourteenth Fourteenth, TFifteenth Fifteenth, TSixteenth Sixteenth)>(
                Expression.Call(
                    null,
                    new Func<IQbservable<TFirst>, IObservable<TSecond>, IObservable<TThird>, IObservable<TFourth>, IObservable<TFifth>, IObservable<TSixth>, IObservable<TSeventh>, IObservable<TEighth>, IObservable<TNinth>, IObservable<TTenth>, IObservable<TEleventh>, IObservable<TTwelfth>, IObservable<TThirteenth>, IObservable<TFourteenth>, IObservable<TFifteenth>, IObservable<TSixteenth>, IQbservable<(TFirst First, TSecond Second, TThird Third, TFourth Fourth, TFifth Fifth, TSixth Sixth, TSeventh Seventh, TEighth Eighth, TNinth Ninth, TTenth Tenth, TEleventh Eleventh, TTwelfth Twelfth, TThirteenth Thirteenth, TFourteenth Fourteenth, TFifteenth Fifteenth, TSixteenth Sixteenth)>>(CombineLatest<TFirst, TSecond, TThird, TFourth, TFifth, TSixth, TSeventh, TEighth, TNinth, TTenth, TEleventh, TTwelfth, TThirteenth, TFourteenth, TFifteenth, TSixteenth>).Method,
                    first.Expression,
                    GetSourceExpression(second),
                    GetSourceExpression(third),

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