Crash with an explicit message when no data was extracted

atr_data_generator/extract/base.py

@@ -192,6 +192,10 @@ class DataGenerator:
             for parent_element in get_children(folder_id, type=self.select.parent_type):
                 self.process_parent(parent_element, partition)
 
+        assert sum(
+            len(partition.values()) for partition in self.data.values()
+        ), "No data was extracted from all three train/validation/test folders."
+
         self.export()
 
         export_parameters(