Servicestack.Redis ArgumentNullException

I regularly see this exception in our logs. It does not happen every time, but quite frequently. Can anyone provide any explanation as to what might be causing it? ServiceStack.Redis V5.9.0, .Net Framework 4.7.2

              TAS.Processor.CleanupService (null) (null) - CleanupService timer threw an exception

System.ArgumentNullException: String reference not set to an instance of a String.
Parameter name: s
at System.Text.Encoding.GetBytes(String s)
at ServiceStack.Redis.RedisClient.HashContainsEntry(String hashId, String key) in C:\BuildAgent\work\b2a0bfe2b1c9a118\src\ServiceStack.Redis\RedisClient_Hash.cs:line 101
at ServiceStack.Redis.Generic.RedisTypedClient1.HashContainsEntry[TKey](IRedisHash2 hash, TKey key) in C:\BuildAgent\work\b2a0bfe2b1c9a118\src\ServiceStack.Redis\Generic\RedisTypedClient_Hash.cs:line 29
at ServiceStack.Redis.Generic.RedisClientHash2.ContainsKey(TKey key) in C:\BuildAgent\work\b2a0bfe2b1c9a118\src\ServiceStack.Redis\Generic\RedisClientHash.Generic.cs:line 99 at ServiceStack.Redis.Generic.RedisClientHash2.TryGetValue(TKey key, T& value) in C:\BuildAgent\work\b2a0bfe2b1c9a118\src\ServiceStack.Redis\Generic\RedisClientHash.Generic.cs:line 114
at TAS.Storage.StateManager.Get[T](String key) in C:\Wayside\Systest\TAS Software\V1.6.1a\TAS.Storage\StateManager.cs:line 259
at TAS.Processor.DataService.GetManagerControllingArea(String areaName) in C:\Wayside\Systest\TAS Software\V1.6.1a\TAS.Processor\DataService.cs:line 917
at TAS.Processor.TasProcessorController.DisconnectingClient(Object sender, String toaUid) in C:\Wayside\Systest\TAS Software\V1.6.1a\TAS.Processor\TasProcessorController.cs:line 187
at TAS.Processor.CleanupService.ClearClient(String clientId) in C:\Wayside\Systest\TAS Software\V1.6.1a\TAS.Processor\CleanupService.cs:line 52
at System.Collections.Generic.List1.ForEach(Action1 action)
at TAS.Processor.CleanupService.CheckForCleanup(Object sender, ElapsedEventArgs e) in C:\Wayside\Systest\TAS Software\V1.6.1a\TAS.Processor\CleanupService.cs:line 78

Looks like the provided key you are passing to the method is null and getting caught when performing HExists here or specifically when trying to convert the key to Utf8Bytes -> https://github.com/ServiceStack/ServiceStack.Redis/blob/d3b7d68dfcd90048f2682476553edfa1aea88c38/src/ServiceStack.Redis/RedisClient_Hash.cs#L111

Are you performing a null check for the provided key at TAS.Storage.StateManager.Get?