Hole in data gets filled in when exporting data

Hi Everybody,
i’ve got an 2d surface of a pressure field around multiple different shaped objects. To further analyze this pressure field, i need to export the data to use it in python for example. In Paraview the objects are just holes in the data, because just the pressure field around the objects is representing. When exporting the data i was expecting a NaN-value or something similar for these holes, but where the holes used to be, are now out of nowhere values, which make my further analyzing incredibly annoying. I have no idea, why the exporting incl. the holes wont work. Anybody an idea?
Best wishes!