[CXF-6058] NPE guard in Header logging

Conflicts:
	rt/transports/http/src/main/java/org/apache/cxf/transport/http/Headers.java
[CXF-6041] Allow deactive/shutdown to proceed without exception if the POA is already deactivated.
[CXF-6068] Use XMLEventFactory.newInstance instead of newFactory due to old stax-api jars being picked up.
[CXF-6030] Add an NPE guard and remove "null" headers
Recording .gitmergeinfo Changes