Allow IPython to start when PYTHONOPTIMIZE=2

Closes gh-8971

IPython/utils/py3compat.py

@@ -47,7 +47,9 b' def _modify_str_or_docstring(str_change_func):'
             func = func_or_str
             doc = func.__doc__
         
-        doc = str_change_func(doc)
+        # PYTHONOPTIMIZE=2 strips docstrings, so they can disappear unexpectedly
+        if doc is not None:
+            doc = str_change_func(doc)
         
         if func:
             func.__doc__ = doc