Java: Fix CFG to include exhaustiveness requirement.

Author: aschackmull

java/ql/lib/semmle/code/java/ControlFlowGraph.qll

@@ -449,10 +449,17 @@ private module Input implements InputSig1, InputSig2 {
   predicate matchAll(Ast::Case c) {
     c instanceof DefaultCase
     or
-    // Switch expressions must be exhaustive, so the last case matches all remaining values
-    exists(SwitchExpr switchExpr, int last |
-      switchExpr.getCase(last) = c and
-      not exists(switchExpr.getCase(last + 1))
+    // Switch expressions and enhanced switch blocks (those that use pattern
+    // cases or match null) must be exhaustive, so the last case matches all
+    // remaining values.
+    // See https://docs.oracle.com/javase/specs/jls/se21/html/jls-14.html#jls-14.11.2
+    exists(Ast::Switch switch, int last |
+      switch instanceof SwitchExpr or
+      exists(switch.(SwitchStmt).getAPatternCase()) or
+      switch.(SwitchStmt).hasNullCase()
+    |
+      switch.getCase(last) = c and
+      not exists(switch.getCase(last + 1))
     )
     or
     c.(J::PatternCase).getAPattern().getType() instanceof TypeObject