C++ Address-of nullchecking

Impl& impl;

That little motherfucking line of code in a header is pissing me off.  Why?  Because it eventually causes an access violation at the line:

if(!impl.mProcessTimer.checkExpirationAndReset(SECS_BETWEEN_PROCESS))

And I have no idea how to check for nulls in an address-of situation.  Regular pointers?  Sure, but whenever I try if(!impl) or some other more convoluted variation of that, MSVC screams about invalid operators. 

Halp plz.

Thing is, it's not my code.  I'm modding Second Life in order to bypass hardware bans, and >>1 is fresh out of their trunk SVN.  This is released software, too, so I don't get wtf is going on.

Compiling with Visual C++ 2005 Express since cross-compiling on Lunix fails for some reason.