There is not reproducer for this currently.

Its a case of implied or shared usage between a function and the code that uses it.  This function is only used in the Python core, so unless
it is used incorrectly, by a python extension or modification, it may never hit the error condition.

The case where this will fail is if for some reason it is called with
a 'endchar' other than '\0'.  The function assumes end char will be '\0', ')', ']', and ']'.