Error while rendering Liquid template CSharp/Client.Class

NSwagStudio version v13.0.5.0 (x64). Doesn't matter if I deselect client, exception or DTO generation. Also happens when trying to generate TypeScript client.

Schema: https://dx-api-au1.thingpark.com/core/latest/tpdx-core-api-contract.json

Exception:

System.InvalidOperationException: Error while rendering Liquid template CSharp/Client.Class: 
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object.

Runtime: NetCore22
   at NSwag.CodeGeneration.Models.OperationModelBase`2.get_UnwrappedResultType() in C:\projects\nswag\src\NSwag.CodeGeneration\Models\OperationModelBase.cs:line 120
   at NSwag.CodeGeneration.CSharp.Models.CSharpOperationModel.get_ResultType() in C:\projects\nswag\src\NSwag.CodeGeneration.CSharp\Models\CSharpOperationModel.cs:line 131
   --- End of inner exception stack trace ---
   at DotLiquid.Context.HandleError(Exception ex)
   at DotLiquid.Block.RenderAll(List`1 list, Context context, TextWriter result)
   at DotLiquid.Document.Render(Context context, TextWriter result)
   at DotLiquid.Template.RenderInternal(TextWriter result, RenderParameters parameters)
   at DotLiquid.Template.Render(TextWriter writer, RenderParameters parameters)
   at DotLiquid.Template.Render(RenderParameters parameters)
   at NJsonSchema.CodeGeneration.DefaultTemplateFactory.LiquidTemplate.Render() ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at NSwag.CodeGeneration.Models.OperationModelBase`2.get_UnwrappedResultType() in C:\projects\nswag\src\NSwag.CodeGeneration\Models\OperationModelBase.cs:line 120
   at NSwag.CodeGeneration.CSharp.Models.CSharpOperationModel.get_ResultType() in C:\projects\nswag\src\NSwag.CodeGeneration.CSharp\Models\CSharpOperationModel.cs:line 131
   --- End of inner exception stack trace ---
   at DotLiquid.Context.HandleError(Exception ex)
   at DotLiquid.Block.RenderAll(List`1 list, Context context, TextWriter result)
   at DotLiquid.Document.Render(Context context, TextWriter result)
   at DotLiquid.Template.RenderInternal(TextWriter result, RenderParameters parameters)
   at DotLiquid.Template.Render(TextWriter writer, RenderParameters parameters)
   at DotLiquid.Template.Render(RenderParameters parameters)
   at NJsonSchema.CodeGeneration.DefaultTemplateFactory.LiquidTemplate.Render()
   --- End of inner exception stack trace ---
   at NJsonSchema.CodeGeneration.DefaultTemplateFactory.LiquidTemplate.Render()
   at NSwag.CodeGeneration.CSharp.CSharpClientGenerator.GenerateClientTypes(String controllerName, String controllerClassName, IEnumerable`1 operations)+MoveNext()
   at System.Collections.Generic.List`1.AddEnumerable(IEnumerable`1 enumerable)
   at System.Collections.Generic.List`1.InsertRange(Int32 index, IEnumerable`1 collection)
   at NSwag.CodeGeneration.ClientGeneratorBase`3.GenerateAllClientTypes() in C:\projects\nswag\src\NSwag.CodeGeneration\ClientGeneratorBase.cs:line 112
   at NSwag.CodeGeneration.ClientGeneratorBase`3.GenerateFile(ClientGeneratorOutputType outputType) in C:\projects\nswag\src\NSwag.CodeGeneration\ClientGeneratorBase.cs:line 73
   at NSwag.Commands.CodeGeneration.SwaggerToCSharpClientCommand.<RunAsync>b__83_0() in C:\projects\nswag\src\NSwag.Commands\Commands\CodeGeneration\OpenApiToCSharpClientCommand.cs:line 242
   at NSwag.Commands.CodeGeneration.SwaggerToCSharpClientCommand.RunAsync() in C:\projects\nswag\src\NSwag.Commands\Commands\CodeGeneration\OpenApiToCSharpClientCommand.cs:line 228
   at NSwag.Commands.CodeGeneration.SwaggerToCSharpClientCommand.RunAsync(CommandLineProcessor processor, IConsoleHost host) in C:\projects\nswag\src\NSwag.Commands\Commands\CodeGeneration\OpenApiToCSharpClientCommand.cs:line 217
   at NSwag.Commands.NSwagDocument.ExecuteAsync() in C:\projects\nswag\src\NSwag.Commands\NSwagDocument.cs:line 85
   at NSwag.Commands.Document.ExecuteDocumentCommand.ExecuteDocumentAsync(IConsoleHost host, String filePath) in C:\projects\nswag\src\NSwag.Commands\Commands\Document\ExecuteDocumentCommand.cs:line 85
   at NSwag.Commands.Document.ExecuteDocumentCommand.RunAsync(CommandLineProcessor processor, IConsoleHost host) in C:\projects\nswag\src\NSwag.Commands\Commands\Document\ExecuteDocumentCommand.cs:line 32
   at NConsole.CommandLineProcessor.ProcessSingleAsync(String[] args, Object input)
   at NConsole.CommandLineProcessor.ProcessAsync(String[] args, Object input)
   at NConsole.CommandLineProcessor.Process(String[] args, Object input)
   at NSwag.Commands.NSwagCommandProcessor.Process(String[] args) in C:\projects\nswag\src\NSwag.Commands\NSwagCommandProcessor.cs:line 56