One difference between the previous if(){} block and this new code is that a put() wasn't called if the key was going to be null.  On the read side this looks the same, but I generally find it easier to understand what is going on with the if(){} block.

Fwiw, I'm not a big fan of tertiaries, they condense the code a bit, but don't actually change the number of branch calls.  When embedded like this, they tend to make the reader step back and think for a moment to understand the actual flow.  In this case, they have to think and say, "ah, if the cache key is null, then it's going to insert a null, which is essentially the same as not inserting anything, so it's a noop if it's null."