[Boost-users] Meaning of "unspecified" arguments (scoped_lock constructors)

Hello, I haven't been able to discover the meaning of "unspecified" in things like scoped_lock constructor parameters: http://www.boost.org/doc/libs/1_36_0/doc/html/boost/interprocess/scoped_lock... I'm trying to lock a scoped lock only if the mutex is not null. It looks like I need to use one of these "unspecified" constructors to assign the mutex but not lock it, so that I can then lock it in an "if" statement if the mutex is not null. I'd be grateful for any help.