crash fix when using a custom dmp_path regex

[wynnw]

• This prevents a crash if the dmp_path regex captures a None value for the dmp_urlparams matching group. A regex like:

^(org.(?P[_a-zA-Z0-9-]+)/)?(?P<dmp_page>[_a-zA-Z0-9-]+)(.?P<dmp_function>[_a-zA-Z0-9.-]+)?/(?P<dmp_urlparams>.+?)?$

for a path like: org.agency-1/agent_dashboard/

would result in the crash.