There should be no error in this program.

$ cat -n T.java
     1 class T { boolean z;
     2 void f() {
     3 final boolean x;
     4 assert z : (x = z) ;
     5 x = false;
     6 }
     7 }
$ newjavac -source 1.4 T.java
T.java:5: variable x might already have been assigned to
        x = false;
        ^
1 error
$