Request textDocument/completion failed in IDE

[keyboardDrummer]

type Path
const HeaderPath: Path
const FooterPath: Path
const input: Input
const largeResult: seq<CryptoItem>

class CryptoItem {
  var key: Path
}

class Input {
  var encryptedStructure: seq<CryptoItem>
}

function SeqFilter<T>(f: T -> bool, xs: seq<T>): seq<T // <-- exception occurs when typing T here

method Foo() {
  var HeaderPaths : seq<Path> := [HeaderPath, FooterPath];

  assert forall k <- input.encryptedStructure :: (exists x :: x in largeResult && x.key == k.key);
  var smallResult := SeqFilter((x : CryptoItem) => x.key !in HeaderPaths, largeResult);
  assert !exists x :: x in smallResult && x.key == HeaderPath;
  assert !exists x :: x in smallResult && x.key == FooterPath;

  assert forall k <- input.encryptedStructure | k.key !in HeaderPaths ::
          (exists x :: x in smallResult && x.key == k.key);
}

[Trace - 5:48:10 PM] Received response 'textDocument/completion - (1166)' in 4ms. Request failed: Internal Error - System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Dafny.NodeExtensions.FindNodeChain(INode node, DafnyPosition position, LList`1 parent, Func`2 predicate)
   at Microsoft.Dafny.NodeExtensions.FindNodeChain(INode node, DafnyPosition position, LList`1 parent, Func`2 predicate)
   at Microsoft.Dafny.NodeExtensions.FindNodeChain(INode node, DafnyPosition position, LList`1 parent, Func`2 predicate)
   at Microsoft.Dafny.NodeExtensions.FindNodeChain(INode node, Uri uri, DafnyPosition position, LList`1 parent, Func`2 predicate)
   at Microsoft.Dafny.NodeExtensions.FindNodeChain(INode node, Uri uri, DafnyPosition position, LList`1 parent, Func`2 predicate)
   at Microsoft.Dafny.NodeExtensions.FindNodeChain(INode node, Uri uri, DafnyPosition position, LList`1 parent, Func`2 predicate)
   at Microsoft.Dafny.NodeExtensions.FindNodeChain(INode node, Uri uri, DafnyPosition position, LList`1 parent, Func`2 predicate)
   at Microsoft.Dafny.NodeExtensions.FindNode[T](INode root, Uri uri, DafnyPosition position)
   at Microsoft.Dafny.LanguageServer.Handlers.DafnyCompletionHandler.CompletionProcessor.IsDotExpression()
   at Microsoft.Dafny.LanguageServer.Handlers.DafnyCompletionHandler.CompletionProcessor.Process()
   at Microsoft.Dafny.LanguageServer.Handlers.DafnyCompletionHandler.Handle(CompletionParams request, CancellationToken cancellationToken)
   at OmniSharp.Extensions.LanguageServer.Server.Pipelines.SemanticTokensDeltaPipeline`2.Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate`1 next)
   at OmniSharp.Extensions.LanguageServer.Server.Pipelines.ResolveCommandPipeline`2.Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate`1 next)
   at MediatR.Pipeline.RequestPreProcessorBehavior`2.Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate`1 next)
   at MediatR.Pipeline.RequestPostProcessorBehavior`2.Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate`1 next)
   at MediatR.Pipeline.RequestExceptionProcessorBehavior`2.Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate`1 next)
   at MediatR.Pipeline.RequestExceptionProcessorBehavior`2.Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate`1 next)
   at MediatR.Pipeline.RequestExceptionActionProcessorBehavior`2.Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate`1 next)
   at MediatR.Pipeline.RequestExceptionActionProcessorBehavior`2.Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate`1 next)
   at OmniSharp.Extensions.JsonRpc.RequestRouterBase`1.<RouteRequest>g__InnerRoute|7_0(IServiceScopeFactory serviceScopeFactory, Request request, TDescriptor descriptor, Object params, CancellationToken token, ILogger logger)
   at OmniSharp.Extensions.JsonRpc.RequestRouterBase`1.RouteRequest(IRequestDescriptor`1 descriptors, Request request, CancellationToken token)
   at OmniSharp.Extensions.JsonRpc.DefaultRequestInvoker.<>c__DisplayClass10_0.<<RouteRequest>b__5>d.MoveNext() (-32603).
[Error - 5:48:10 PM] Request textDocument/completion failed.
  Message: Internal Error - System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Dafny.NodeExtensions.FindNodeChain(INode node, DafnyPosition position, LList`1 parent, Func`2 predicate)