Minor fix to accommodate null descriptions and parents with no attributes

# Conflicts:
#	src/ifcopenshell-python/ifcopenshell/util/doc.py

src/blenderbim/blenderbim/bim/helper.py

@@ -130,7 +130,7 @@ def add_attribute_enum_items_descriptions(attribute_blender, enum_items):
     for enum_item in enum_items:
         new_enum_description = attribute_blender.enum_descriptions.add()
         try:
-            description = get_predefined_type_doc(version, attribute_blender.ifc_class, enum_item)
+            description = get_predefined_type_doc(version, attribute_blender.ifc_class, enum_item) or ""
         except KeyError:  # TODO this only supports predefined type enums. Add support for other types of enums ?
             description = ""
         new_enum_description.name = description

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

@@ -93,7 +93,7 @@ def get_entity_doc(version, entity_name, recursive=True):
             parent_entity = get_entity_doc(version, ifc_supertype.name(), recursive=True)
             if "attributes" not in entity:
                 entity["attributes"] = dict()
-            for parent_attr in parent_entity["attributes"]:
+            for parent_attr in parent_entity.get("attributes", []):
                 entity["attributes"][parent_attr] = parent_entity["attributes"][parent_attr]
         return entity
 

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

@@ -376,6 +376,7 @@ def get_decomposition(element):
             results.append(rel.RelatedBuildingElement)
     return results
 
+
 def get_grouped_by(element):
     """
     Retrieves all subelements of an element based on the group.
@@ -396,7 +397,8 @@ def get_grouped_by(element):
             queue.extend(rel.RelatedObjects)
             results.extend(rel.RelatedObjects)
     return results
-    
+
+
 def get_aggregate(element):
     """
     Retrieves the aggregate of an element.