Java: Fix bug in nullness

Author: aschackmull

java/ql/lib/semmle/code/java/dataflow/Nullness.qll

@@ -653,7 +653,7 @@ private Expr trackingVarGuard(
       result = integerGuard(trackvar.getAnAccess(), branch, k, isA)
       or
       exists(int k2 |
-        result = integerGuard(trackvar.getAnAccess(), branch.booleanNot(), k2, true) and
+        result = integerGuard(trackvar.getAnAccess(), branch, k2, true) and
         isA = false and
         k2 != k
       )

java/ql/test/query-tests/Nullness/B.java

@@ -513,6 +513,6 @@ public void trackTest(Object o, int n) {
     int c = -1;
     if (maybe) { }
     if (c == 100) { return; }
-    o.hashCode(); // NPE - false negative
+    o.hashCode(); // NPE
   }
 }

java/ql/test/query-tests/Nullness/NullMaybe.expected

@@ -21,6 +21,7 @@
 | B.java:448:9:448:9 | x | Variable $@ may be null at this access because of $@ assignment. | B.java:442:5:442:28 | Object x | x | B.java:446:9:446:16 | ...=... | this |
 | B.java:465:9:465:9 | x | Variable $@ may be null at this access because of $@ assignment. | B.java:458:5:458:28 | Object x | x | B.java:470:9:470:16 | ...=... | this |
 | B.java:487:9:487:9 | x | Variable $@ may be null at this access because of $@ assignment. | B.java:476:5:476:20 | Object x | x | B.java:476:12:476:19 | x | this |
+| B.java:516:5:516:5 | o | Variable $@ may be null at this access as suggested by $@ null guard. | B.java:511:25:511:32 | o | o | B.java:512:22:512:30 | ... == ... | this |
 | C.java:9:44:9:45 | a2 | Variable $@ may be null at this access as suggested by $@ null guard. | C.java:6:5:6:23 | long[][] a2 | a2 | C.java:7:34:7:54 | ... != ... | this |
 | C.java:9:44:9:45 | a2 | Variable $@ may be null at this access because of $@ assignment. | C.java:6:5:6:23 | long[][] a2 | a2 | C.java:6:14:6:22 | a2 | this |
 | C.java:10:17:10:18 | a3 | Variable $@ may be null at this access as suggested by $@ null guard. | C.java:8:5:8:21 | long[] a3 | a3 | C.java:9:38:9:58 | ... != ... | this |