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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"ArgumentNullException in GetConstantValueAsString crashes process","articleBody":"Having exactly this in a file causes the language server to crash until VSC gives up trying to restart it:\r\n\r\n```python\r\nfrom typing import TypeVar\r\n\r\ndef cla\r\n\r\n_ = TypeVar()\r\n```\r\n\r\nFound while making minimal examples for generics.\r\n\r\n```\r\nAssertion Failed\r\nSystem.ArgumentNullException: Value cannot be null.\r\nParameter name: source\r\n   at System.Linq.Enumerable.Select[TSource,TResult](IEnumerable`1 source, Func`2 selector)\r\n   at Microsoft.PythonTools.Analysis.AnalysisValueSetExtensions.GetConstantValueAsString(IAnalysisSet values) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\AnalysisValueSetExtensions.cs:line 246\r\n   at Microsoft.PythonTools.Analysis.Values.TypingModuleInfo.\u003c\u003ec__DisplayClass6_0.\u003cNewType_Call\u003eb__0(Node n) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Values\\TypingModuleInfo.cs:line 56\r\n   at Microsoft.PythonTools.Analysis.Analyzer.InterpreterScope.GetOrMakeNodeValue(Node node, NodeValueKind kind, Func`2 maker) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Analyzer\\InterpreterScope.cs:line 381\r\n   at Microsoft.PythonTools.Analysis.Values.TypingModuleInfo.NewType_Call(Node node, AnalysisUnit unit, IAnalysisSet[] args, NameExpression[] keywordArgNames) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Values\\TypingModuleInfo.cs:line 55\r\n   at Microsoft.PythonTools.Analysis.Values.SpecializedCallable.Call(Node node, AnalysisUnit unit, IAnalysisSet[] args, NameExpression[] keywordArgNames) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Values\\SpecializedCallable.cs:line 49\r\n   at Microsoft.PythonTools.Analysis.Analyzer.ExpressionEvaluator.EvaluateCall(ExpressionEvaluator ee, Node node) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Analyzer\\ExpressionEvaluator.cs:line 378\r\n   at Microsoft.PythonTools.Analysis.Analyzer.ExpressionEvaluator.EvaluateWorker(Node node) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Analyzer\\ExpressionEvaluator.cs:line 211\r\n   at Microsoft.PythonTools.Analysis.Analyzer.ExpressionEvaluator.Evaluate(Expression node) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Analyzer\\ExpressionEvaluator.cs:line 55\r\n   at Microsoft.PythonTools.Analysis.Analyzer.DDG.Walk(AssignmentStatement node) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Analyzer\\DDG.cs:line 137\r\n   at Microsoft.PythonTools.Parsing.Ast.AssignmentStatement.Walk(PythonWalker walker) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Parsing\\Ast\\AssignmentStatement.cs:line 41\r\n   at Microsoft.PythonTools.Analysis.Analyzer.DDG.Walk(SuiteStatement node) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Analyzer\\DDG.cs:line 665\r\n   at Microsoft.PythonTools.Parsing.Ast.SuiteStatement.Walk(PythonWalker walker) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Parsing\\Ast\\SuiteStatement.cs:line 34\r\n   at Microsoft.PythonTools.Parsing.Ast.PythonAst.Walk(PythonWalker walker) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Parsing\\Ast\\PythonAst.cs:line 92\r\n   at Microsoft.PythonTools.Analysis.AnalysisUnit.AnalyzeWorker(DDG ddg, CancellationToken cancel) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\AnalysisUnit.cs:line 154\r\n   at Microsoft.PythonTools.Analysis.AnalysisUnit.Analyze(DDG ddg, CancellationToken cancel) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\AnalysisUnit.cs:line 139\r\n   at Microsoft.PythonTools.Analysis.Analyzer.DDG.Analyze(Deque`1 queue, CancellationToken cancel, Action`1 reportQueueSize, Int32 reportQueueInterval) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Analyzer\\DDG.cs:line 75\r\n   at Microsoft.PythonTools.Analysis.PythonAnalyzer.AnalyzeQueuedEntries(CancellationToken cancel) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\PythonAnalyzer.cs:line 907\r\n   at Microsoft.PythonTools.Intellisense.AnalysisQueue.GroupAnalysis.Analyze(CancellationToken cancel) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Intellisense\\AnalysisQueue.cs:line 229\r\n   at Microsoft.PythonTools.Intellisense.AnalysisQueue.HandleAnalyzable(IAnalyzable item, AnalysisPriority priority, CancellationToken cancellationToken) in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Intellisense\\AnalysisQueue.cs:line 152\r\n   at Microsoft.PythonTools.Intellisense.AnalysisQueue.ConsumerLoop() in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Intellisense\\AnalysisQueue.cs:line 64\r\n\r\n   at Microsoft.Python.LanguageServer.Implementation.Server.Analysis_UnhandledException(Object sender, UnhandledExceptionEventArgs e) in C:\\Users\\jabaile\\python-language-server\\src\\LanguageServer\\Impl\\Implementation\\Server.cs:line 116\r\n   at Microsoft.PythonTools.Intellisense.AnalysisQueue.ConsumerLoop() in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Intellisense\\AnalysisQueue.cs:line 64\r\n   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)\r\n   at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1.AsyncStateMachineBox`1.MoveNext()\r\n   at System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction(IAsyncStateMachineBox box, Boolean allowInlining)\r\n   at System.Threading.Tasks.Task.RunContinuations(Object continuationObject)\r\n   at System.Threading.Tasks.Task`1.TrySetResult(TResult result)\r\n   at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1.SetExistingTaskResult(TResult result)\r\n   at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1.SetResult(TResult result)\r\n   at Microsoft.PythonTools.Intellisense.AnalysisQueue.ConsumeAsync() in C:\\Users\\jabaile\\python-language-server\\src\\Analysis\\Engine\\Impl\\Intellisense\\AnalysisQueue.cs:line 89\r\n   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)\r\n   at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1.AsyncStateMachineBox`1.MoveNext()\r\n   at System.Threading.ThreadPoolWorkQueue.Dispatch()\r\n```","author":{"url":"https://github.com/jakebailey","@type":"Person","name":"jakebailey"},"datePublished":"2018-11-06T21:01:38.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/353/python-language-server/issues/353"}