Fix remove_drawing crash on corrupted drawing

Fix #8122: Guard get_sheet_references against a missing document reference.
Guard remove_drawing against a missing document association to skip
the document/file cleanup steps. Fall back to direct entity removal
when the drawing's group association is also missing, so the IFC
entity is purged and the Drawings panel refreshes correctly.

Generated with the assistance of an AI coding tool.

src/bonsai/bonsai/core/drawing.py

@@ -412,16 +412,20 @@ def remove_drawing(
             drawing_tool.delete_object(reference_obj)
         ifc.run("root.remove_product", product=reference)
 
-    information = drawing_tool.get_reference_document(drawing_tool.get_drawing_document(drawing))
-    uri = ifc.resolve_uri(drawing_tool.get_document_uri(information))
-    if drawing_tool.does_file_exist(uri):
-        drawing_tool.delete_file(uri)
-    ifc.run("document.remove_information", information=information)
+    drawing_document = drawing_tool.get_drawing_document(drawing)
+    if drawing_document is not None:
+        information = drawing_tool.get_reference_document(drawing_document)
+        uri = ifc.resolve_uri(drawing_tool.get_document_uri(information))
+        if drawing_tool.does_file_exist(uri):
+            drawing_tool.delete_file(uri)
+        ifc.run("document.remove_information", information=information)
 
     group = drawing_tool.get_drawing_group(drawing)
     if group:
         drawing_tool.delete_drawing_elements(drawing_tool.get_group_elements(group))
         ifc.run("group.remove_group", group=group)
+    else:
+        drawing_tool.delete_drawing_elements([drawing])
 
     drawing_tool.import_drawings()
 

src/bonsai/bonsai/tool/drawing.py

@@ -2765,6 +2765,8 @@ class Drawing(bonsai.core.tool.Drawing):
     def get_sheet_references(cls, drawing: ifcopenshell.entity_instance) -> list[ifcopenshell.entity_instance]:
         sheet_references: list[ifcopenshell.entity_instance] = []
         drawing_reference = cls.get_drawing_document(drawing)
+        if drawing_reference is None:
+            return sheet_references
         for sheet in tool.Ifc.get().by_type("IfcDocumentInformation"):
             if not sheet.Scope == "SHEET":
                 continue