NRE from spell checker while working in Roslyn

[tmat]

System.NullReferenceException: Object reference not set to an instance of an object.
      at Roslyn.Utilities.BKTree.Find(TemporaryArray`1& result, String value, Nullable`1 threshold)
      at Roslyn.Utilities.SpellChecker.FindSimilarWords(TemporaryArray`1& similarWords, String value, Boolean substringsAreSimilar)
      at Microsoft.CodeAnalysis.FindSymbols.SymbolTreeInfo.FuzzyFindAsync(AsyncLazy`1 lazyAssembly, String name, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.FindSymbols.SymbolTreeInfo.FindAsync(SearchQuery query, AsyncLazy`1 lazyAssembly, SymbolFilter filter, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.MetadataSymbolsSearchScope.FindDeclarationsAsync(SymbolFilter filter, SearchQuery searchQuery, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.SearchScope.FindDeclarationsAsync(String name, TSimpleNameSyntax nameNode, SymbolFilter filter, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.SymbolReferenceFinder.GetReferencesForMatchingTypesAsync(SearchScope searchScope, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.SymbolReferenceFinder.DoAsync(SearchScope searchScope, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.ProcessReferencesAsync(ConcurrentQueue`1 allSymbolReferences, Int32 maxResults, CancellationTokenSource linkedTokenSource, Task`1 task)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.FindResultsInUnreferencedMetadataSymbolsAsync(ConcurrentDictionary`2 referenceToCompilation, Project project, ConcurrentQueue`1 allSymbolReferences, Int32 maxResults, SymbolReferenceFinder finder, Boolean exact, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.FindResultsAsync(ConcurrentDictionary`2 projectToAssembly, ConcurrentDictionary`2 referenceToCompilation, Project project, Int32 maxResults, SymbolReferenceFinder finder, Boolean exact, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.FindResultsAsync(Document document, SemanticModel semanticModel, String diagnosticId, SyntaxNode node, Int32 maxResults, ISymbolSearchService symbolSearchService, AddImportOptions options, ImmutableArray`1 packageSources, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.GetFixesInCurrentProcessAsync(Document document, TextSpan span, String diagnosticId, Int32 maxResults, ISymbolSearchService symbolSearchService, AddImportOptions options, ImmutableArray`1 packageSources, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.AddImport.AbstractAddImportFeatureService`1.GetFixesAsync(Document document, TextSpan span, String diagnosticId, Int32 maxResults, ISymbolSearchService symbolSearchService, AddImportOptions options, ImmutableArray`1 packageSources, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.RemoteMissingImportDiscoveryService.<>c__DisplayClass3_0.<<GetFixesAsync>b__0>d.MoveNext()
   --- End of stack trace from previous location ---
      at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.<>c__DisplayClass9_0`1.<<RunWithSolutionAsync>g__ProcessSolutionAsync|1>d.MoveNext()
   --- End of stack trace from previous location ---
      at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.RunWithSolutionAsync[T](AssetProvider assetProvider, Checksum solutionChecksum, Int32 workspaceVersion, Boolean updatePrimaryBranch, Func`2 implementation, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.RunWithSolutionAsync[T](AssetProvider assetProvider, Checksum solutionChecksum, Int32 workspaceVersion, Boolean updatePrimaryBranch, Func`2 implementation, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.BrokeredServiceBase.RunWithSolutionAsync[T](Checksum solutionChecksum, Func`2 implementation, CancellationToken cancellationToken)
      at Microsoft.CodeAnalysis.Remote.BrokeredServiceBase.RunServiceImplAsync[T](Func`2 implementation, CancellationToken cancellationToken)