{"record":{"id":"e7eb5a73c59f4d00","repo":"dotnet/reactive","slug":"value-cannot-be-null-parameter-sixth-qbservableex-homoicon","errorCode":null,"errorMessage":"Value cannot be null. (Parameter 'sixth')","messagePattern":"Value cannot be null\\. \\(Parameter 'sixth'\\)","errorType":"validation","errorClass":"ArgumentNullException","httpStatus":null,"severity":"error","filePath":"Rx.NET/Source/src/System.Reactive/Linq/QbservableEx.Homoicon.cs","lineNumber":417,"sourceCode":"        /// <param name=\"ninth\">Ninth observable source.</param>\n        /// <param name=\"tenth\">Tenth observable source.</param>\n        /// <returns>An observable sequence containing the result of combining elements of the sources using tuple values.</returns>\n        /// <exception cref=\"ArgumentNullException\">\n        /// <paramref name=\"first\" /> or <paramref name=\"second\" /> or <paramref name=\"third\" /> or <paramref name=\"fourth\" /> or <paramref name=\"fifth\" /> or <paramref name=\"sixth\" /> or <paramref name=\"seventh\" /> or <paramref name=\"eighth\" /> or <paramref name=\"ninth\" /> or <paramref name=\"tenth\" /> is null.</exception>\n        public static IQbservable<(TFirst First, TSecond Second, TThird Third, TFourth Fourth, TFifth Fifth, TSixth Sixth, TSeventh Seventh, TEighth Eighth, TNinth Ninth, TTenth Tenth)> CombineLatest<TFirst, TSecond, TThird, TFourth, TFifth, TSixth, TSeventh, TEighth, TNinth, TTenth>(this IQbservable<TFirst> first, IObservable<TSecond> second, IObservable<TThird> third, IObservable<TFourth> fourth, IObservable<TFifth> fifth, IObservable<TSixth> sixth, IObservable<TSeventh> seventh, IObservable<TEighth> eighth, IObservable<TNinth> ninth, IObservable<TTenth> tenth)\n        {\n            if (first == null)\n                throw new ArgumentNullException(nameof(first));\n            if (second == null)\n                throw new ArgumentNullException(nameof(second));\n            if (third == null)\n                throw new ArgumentNullException(nameof(third));\n            if (fourth == null)\n                throw new ArgumentNullException(nameof(fourth));\n            if (fifth == null)\n                throw new ArgumentNullException(nameof(fifth));\n            if (sixth == null)\n                throw new ArgumentNullException(nameof(sixth));\n            if (seventh == null)\n                throw new ArgumentNullException(nameof(seventh));\n            if (eighth == null)\n                throw new ArgumentNullException(nameof(eighth));\n            if (ninth == null)\n                throw new ArgumentNullException(nameof(ninth));\n            if (tenth == null)\n                throw new ArgumentNullException(nameof(tenth));\n\n            return first.Provider.CreateQuery<(TFirst First, TSecond Second, TThird Third, TFourth Fourth, TFifth Fifth, TSixth Sixth, TSeventh Seventh, TEighth Eighth, TNinth Ninth, TTenth Tenth)>(\n                Expression.Call(\n                    null,\n                    new Func<IQbservable<TFirst>, IObservable<TSecond>, IObservable<TThird>, IObservable<TFourth>, IObservable<TFifth>, IObservable<TSixth>, IObservable<TSeventh>, IObservable<TEighth>, IObservable<TNinth>, IObservable<TTenth>, IQbservable<(TFirst First, TSecond Second, TThird Third, TFourth Fourth, TFifth Fifth, TSixth Sixth, TSeventh Seventh, TEighth Eighth, TNinth Ninth, TTenth Tenth)>>(CombineLatest<TFirst, TSecond, TThird, TFourth, TFifth, TSixth, TSeventh, TEighth, TNinth, TTenth>).Method,\n                    first.Expression,\n                    GetSourceExpression(second),\n                    GetSourceExpression(third),\n                    GetSourceExpression(fourth),\n                    GetSourceExpression(fifth),","sourceCodeStart":399,"sourceCodeEnd":435,"githubUrl":"https://github.com/dotnet/reactive/blob/94b5d5ab912789f5abe9a72138a25bbd716fe59c/Rx.NET/Source/src/System.Reactive/Linq/QbservableEx.Homoicon.cs#L399-L435","documentation":"ArgumentNullException with message \"Value cannot be null. (Parameter 'sixth')\" is thrown by the 10-source CombineLatest overload when the sixth source sequence is null. Rx operators validate inputs eagerly; a null source would produce an invalid expression tree when CombineLatest attempts first.Provider.CreateQuery, so the null check at QbservableEx.Homoicon.cs:417-418 throws immediately.","triggerScenarios":"Calling QbservableEx.CombineLatest with sixth == null; the guard executes after sources one through five pass validation.","commonSituations":"Dynamically composed stream lists where one element is null; a service or repository returning null instead of an observable; incorrect merge logic building the argument list programmatically.","solutions":["Pass a real IObservable<TSixth>; substitute Observable.Empty<TSixth>() or Observable.Never<TSixth>() when the stream is optional.","Fix the producer or composition code that yields a null sixth source.","Reduce arity: use an overload with fewer sources rather than padding with null."],"exampleFix":"// before\nvar combined = first.CombineLatest(second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth);\n// after\nvar combined = first.CombineLatest(second, third, fourth, fifth, sixth ?? Observable.Empty<TSixth>(), seventh, eighth, ninth, tenth);","handlingStrategy":"validation","validationCode":"if (sixth is null) throw new InvalidOperationException(\"sixth source must be a non-null IObservable<TSixth>\");\n// or: sixth ??= Observable.Empty<TSixth>();","typeGuard":"static bool IsValidSource<T>(IObservable<T>? source) => source is not null;","tryCatchPattern":"try\n{\n    var combined = first.CombineLatest(second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth);\n}\ncatch (ArgumentNullException ex) when (ex.ParamName == \"sixth\")\n{\n    // handle missing sixth source\n}","preventionTips":["When assembling source lists programmatically, filter out or replace null elements before composing.","Coalesce optional sources with ?? Observable.Empty<T>().","Fix producers that return null instead of throwing a meaningful error."],"tags":["argument-null","reactive-extensions","combinelatest","qbservable","validation"],"backgroundTag":"null-argument","analyzedSha":"94b5d5ab912789f5abe9a72138a25bbd716fe59c","analyzedAt":"2026-09-15T02:26:24.759Z","contentChangedAt":"2026-09-15T02:26:24.759Z","schemaVersion":2},"datasetVersion":"2026-09-15T23:17:13.987Z"}