System.Collections.Generic.KeyNotFoundException : An index satisfying the predicate was not found in the collection.
   at Microsoft.FSharp.Collections.SeqModule.loop@1146-22[T](FSharpFunc`2 predicate,IEnumerator`1 ie,Int32 i)
   at Microsoft.FSharp.Collections.SeqModule.FindIndex[T](FSharpFunc`2 predicate,IEnumerable`1 source)
   at Microsoft.VisualStudio.FSharp.Editor.AddOpenCodeFixProvider.getOpenDeclaration(SourceText sourceText,InsertionContext ctx,String ns)
   at Microsoft.VisualStudio.FSharp.Editor.AddOpenCodeFixProvider.openNamespaceFix(InsertionContext ctx,String name,String ns,Boolean multipleNames,SourceText sourceText)
   at <StartupCode$FSharp-Editor>[email protected](Tuple`4 tupledArg)
   at Microsoft.FSharp.Collections.Internal.IEnumerator.map@128.DoMoveNext(b& curr)
   at Microsoft.FSharp.Collections.Internal.IEnumerator.MapEnumerator`1.System.Collections.IEnumerator.MoveNext()
   at Microsoft.FSharp.Core.CompilerServices.RuntimeHelpers.takeInner@312[T,TResult](ConcatEnumerator`2 x,Unit unitVar0)
   at Microsoft.FSharp.Collections.SeqModule.TryHead[T](IEnumerable`1 source)
   at async StartupCode$FSharp-Editor(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.VisualStudio.FSharp.Editor.CodeFixExtensions.CodeFixContext-RegisterFsharpFix@108(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.CodeAnalysis.CodeFixes.CodeFixService.GetCodeFixesAsync(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.CodeAnalysis.Extensions.IExtensionManagerExtensions.PerformFunctionAsync[T](<Unknown Parameters>)