Unhandled Exception: System.ArgumentNullException: Value cannot be null. Parameter name: key

Question

This is the error message I get. The application uses MySQL 8.0.33. I have upgraded it from a previous version. I use MySQL.Data, MySQL.Web, MySQL.DataEntityFramework. The first one is listed as version 8.0.33. The others are listed as 8.0.20, and I haven't been able to figure out how to get them upgraded. I made no changes to any DB code so the only difference is the version number of the two items. On the two items, there is a yellow triangle so something is up, but I can't figure out what. The lack of a line of code isn't helping either.

I couldn't just tag MySQL, so I had to use the one I did.

Unhandled Exception: System.ArgumentNullException: Value cannot be null.
Parameter name: key
   at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
   at System.Collections.Generic.Dictionary`2.FindEntry(TKey key)
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at MySql.Data.MySqlClient.MySqlPoolManager.<CleanIdleConnections>d__28.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()