handle when no signatures are found

IPython/core/completer.py

@@ -990,6 +990,10 b' def _make_signature(completion)-> str:'
 
     # it looks like this might work on jedi 0.17
     if hasattr(completion, 'get_signatures'):
+        signatures = completion.get_signatures()
+        if not signatures:
+            return  '(?)'
+
         c0 = completion.get_signatures()[0]
         return '('+c0.to_string().split('(', maxsplit=1)[1]