Unhandled exception: sequence contains no elements

[sebastian]

fail: Microsoft.AspNetCore.Server.Kestrel[13]
      Connection id "0HM1O9UPLD5VH", Request id "0HM1O9UPLD5VH:0000000A": An unhandled exception was thrown by the application.
System.InvalidOperationException: Sequence contains no elements
   at System.Linq.ThrowHelper.ThrowNoElementsException()
   at System.Linq.Enumerable.Max[TSource](IEnumerable`1 source, Func`2 selector)
   at Explorer.Exploration.get_SampleData()+MoveNext() in /Users/sebastian/work-projects/explorer/src/explorer/Exploration.cs:line 42
   at System.Text.Json.JsonSerializer.HandleEnumerable(JsonClassInfo elementClassInfo, JsonSerializerOptions options, Utf8JsonWriter writer, WriteStack& state)
   at System.Text.Json.JsonSerializer.Write(Utf8JsonWriter writer, Int32 originalWriterDepth, Int32 flushThreshold, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.JsonSerializer.WriteAsyncCore(Stream utf8Json, Object value, Type inputType, JsonSerializerOptions options, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter.WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
   at Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter.WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|29_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Sentry.AspNetCore.SentryMiddleware.InvokeAsync(HttpContext context)
   at Sentry.AspNetCore.SentryMiddleware.InvokeAsync(HttpContext context)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1 application)

I can consistently reproduce this error by analyzing the customers table in the local test data source cloak_postgres_native.

It's a table containing nothing but a user_id column, which gets filtered out before the request is made, hence presumably explorer is asked to analyze a table with no columns.

[sebastian]

Maybe this can be reproduced by calling the API with an empty column list?

Like

curl -k -X POST -H "Content-Type: application/json" http://localhost:5000/api/v1/explore \
  -d "{
   \"ApiUrl\":\"https://attack.aircloak.com/api/\"
   \"ApiKey\":\"my_secret_key\",
   \"DataSource\": \"gda_banking\",
   \"Table\":\"loans\",
   \"Columns\":[]
   }"