Fix bug to prevent users from appending a project library asset twice

src/blenderbim/blenderbim/bim/import_ifc.py

@@ -153,7 +153,7 @@ class IfcImporter:
         self.settings_native.set(self.settings_native.INCLUDE_CURVES, True)
         self.settings_2d = ifcopenshell.geom.settings()
         self.settings_2d.set(self.settings_2d.INCLUDE_CURVES, True)
-        self.filter_mode = "BLACKLIST"
+        self.filter_mode = None
         self.include_elements = set()
         self.exclude_elements = set()
         self.project = None

src/blenderbim/blenderbim/bim/module/project/operator.py

@@ -326,6 +326,8 @@ class AppendLibraryElement(bpy.types.Operator):
             library=IfcStore.library_file,
             element=IfcStore.library_file.by_id(self.definition),
         )
+        if not element:
+            return {"FINISHED"}
         self.import_type_from_ifc(element, context)
         blenderbim.bim.handler.purge_module_data()
         return {"FINISHED"}