Redis Null exception #10

System.ArgumentException: A null key is not valid in this context
at StackExchange.Redis.RedisKey.AssertNotNull() in //src/StackExchange.Redis/RedisKey.cs:line 171
at StackExchange.Redis.RedisDatabase.StringGet(RedisKey key, CommandFlags flags) in //src/StackExchange.Redis/RedisDatabase.cs:line 2374
at CoviDok.Data.SessionProviders.RedisProvider.Get(String key) in /src/gitea-bme_covidok-backend_master/CoviDok/Data/SessionProviders/RedisProvider.cs:line 26
at CoviDok.BLL.Sessions.SessionHandler.GetSession(String SessionId) in /src/gitea-bme_covidok-backend_master/CoviDok/BLL/Sessions/SessionHandler.cs:line 31
at CoviDok.Controllers.AssistantController.PutAssistant(Int32 id, PublicAssistant ast) in /src/gitea-bme_covidok-backend_master/CoviDok/Controllers/AssistantController.cs:line 40
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask1 actionResultValueTask) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync() --- End of stack trace from previous location where exception was thrown --- at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync() --- End of stack trace from previous location where exception was thrown --- at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope) at Microsoft.AspNetCore.Builder.RouterMiddleware.Invoke(HttpContext httpContext) at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication1 application)

System.ArgumentException: A null key is not valid in this context at StackExchange.Redis.RedisKey.AssertNotNull() in /_/src/StackExchange.Redis/RedisKey.cs:line 171 at StackExchange.Redis.RedisDatabase.StringGet(RedisKey key, CommandFlags flags) in /_/src/StackExchange.Redis/RedisDatabase.cs:line 2374 at CoviDok.Data.SessionProviders.RedisProvider.Get(String key) in /src/gitea-bme_covidok-backend_master/CoviDok/Data/SessionProviders/RedisProvider.cs:line 26 at CoviDok.BLL.Sessions.SessionHandler.GetSession(String SessionId) in /src/gitea-bme_covidok-backend_master/CoviDok/BLL/Sessions/SessionHandler.cs:line 31 at CoviDok.Controllers.AssistantController.PutAssistant(Int32 id, PublicAssistant ast) in /src/gitea-bme_covidok-backend_master/CoviDok/Controllers/AssistantController.cs:line 40 at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync() --- End of stack trace from previous location where exception was thrown --- at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync() --- End of stack trace from previous location where exception was thrown --- at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope) at Microsoft.AspNetCore.Builder.RouterMiddleware.Invoke(HttpContext httpContext) at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1 application)