diff --git a/docs/_extend_docstrings.py b/docs/_extend_docstrings.py
index 21072976c..c1527b070 100644
--- a/docs/_extend_docstrings.py
+++ b/docs/_extend_docstrings.py
@@ -720,8 +720,10 @@ def _create_latex_doit_definition(expr: sp.Expr, deep: bool = False) -> str:
 
 
 def _append_to_docstring(class_type: Callable | type, appended_text: str) -> None:
-    assert class_type.__doc__ is not None
-    class_type.__doc__ += appended_text
+    if class_type.__doc__ is None:
+        class_type.__doc__ = appended_text
+    else:
+        class_type.__doc__ += appended_text
 
 
 def __generate_transitions_cached(