I already made a similar post about this topic, i applied all the changes they told me and tried their approaches, but it still didnt work (link:

so I actually run your code and it throws an exception

so your model is wrong you need to fix that property to be double or float

Public Property Gewicht As Double?

after that it works

the fact that you did not mention an exception tells my you either are ignoring them or you just have written a try catch that hides them. Remove that if it exists. Exceptions are there to help you know what is going on. Also it is useful to stop VS on exceptions at the line they are thrown you can make that by checking the checkbox in this window: