What does it mean? Could you help me please to understand how I can solve this problem

Revit
,
1

The input argument “document” of the `anonymous-namespace’::FilteredElementCollector_constructor function or one element in the collection is null on line 326 of the file d:\ship\2018_px64\source\revit\revitdbapi\APIFilteredElementCollectorPro Parameter name: document

2

My guess is that you haven’t set up your inputs correctly. Can you post your sample code for review?