face: introduce NullTransport and use it in several places

Refs: #4528
Change-Id: Icc7a77232bca1a700ce1319493c15a85d05d7488
diff --git a/docs/doxygen.conf.in b/docs/doxygen.conf.in
index 7928d8c..5ca87f3 100644
--- a/docs/doxygen.conf.in
+++ b/docs/doxygen.conf.in
@@ -2061,6 +2061,7 @@
                          PUBLIC_WITH_TESTS_ELSE_PROTECTED=protected \
                          PUBLIC_WITH_TESTS_ELSE_PRIVATE=private \
                          PROTECTED_WITH_TESTS_ELSE_PRIVATE=private \
+                         OVERRIDE_WITH_TESTS_ELSE_FINAL=final \
                          FINAL_UNLESS_WITH_TESTS=final
 
 # If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this