[develop] fixed uninitialized pointer.

src/mtime_t_event.inc

@@ -308,6 +308,7 @@
     ELSE
       allocate(this%last_event_in_group%nextEventInGroup, source=event_to_add)
       this%last_event_in_group => this%last_event_in_group%nextEventInGroup
+      NULLIFY(this%last_event_in_group%nextEventInGroup)
     ENDIF
   END SUBROUTINE t_eventGroup_addToGroup