xmlRegexpPrint() could crash while trying to print
https://gitlab.gnome.org/GNOME/libxml2/-/blob/master/xmlregexp.c#L5593
xmlRegexpPrint()
tries to print string
member within regexp
without checking for NULL pointers. ISO C doesn't define the behavior of printing NULL strings so some implementations of printf might seg fault the application when accessing this API.
e.g. testAutomata would crash in such scenarios.
a simple check for if it's NULL and if so either skip printing it or explicitly print '(null)' should fix the problem.