Apply suggestion from @aothms

src/ifcopenshell-python/ifcopenshell/util/unit.py

@@ -962,6 +962,7 @@ def convert_file_length_units(ifc_file: ifcopenshell.file, target_units: str = "
         )
 
     unit_assignment = get_unit_assignment(file_patched)
+    # UnitType not available on IfcMonetaryUnit
     unit_assignment.Units = [new_length, *(u for u in unit_assignment.Units if getattr(u, 'UnitType', None) != new_length.UnitType)]
     if not file_patched.get_total_inverses(old_length):
         ifcopenshell.util.element.remove_deep2(file_patched, old_length)