Cannot convert null literal to non-nullable reference type.

Cannot convert null literal to non-nullable reference type.

Possible null reference argument for parameter 'learningContent' in 'LearningElementPe.LearningElementPe(string name, ILearningContentPe learningContent, string description, string goals, LearningElementDifficultyEnum difficulty, ElementModel elementModel, int workload = 0, int points = 1, double positionX = 0, double positionY = 0)'.

'MockedRequestExtensions.Respond(MockedRequest, HttpResponseMessage)' is obsolete: 'Using this overload is not recommended. Instead, use Respond(req => new HttpResponseMessage(...))'

'MockedRequestExtensions.Respond(MockedRequest, HttpResponseMessage)' is obsolete: 'Using this overload is not recommended. Instead, use Respond(req => new HttpResponseMessage(...))'

Non-nullable field '_fileSystem' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the field as nullable.

This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread.

This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread.

Dereference of a possibly null reference.