Fix #1288 - error when importing consecutive files.

src/ifcblenderexport/blenderbim/bim/module/classification/data.py

@@ -12,6 +12,16 @@ class Data:
     library_classifications = {}
     library_references = {}
 
+    @classmethod
+    def purge(cls):
+        cls.is_loaded = False
+        cls.products = {}
+        cls.classifications = {}
+        cls.references = {}
+        cls.library_file = None
+        cls.library_classifications = {}
+        cls.library_references = {}
+
     @classmethod
     def load(cls, product_id=None):
         cls._file = IfcStore.get_file()