Fixed a comparison with null and boolean

Author: cheestree

liquidjava-verifier/src/main/java/liquidjava/processor/refinement_checker/VCChecker.java

@@ -106,7 +106,8 @@ public SMTResult verifySMTSubtype(Predicate expected, Predicate found, SourcePos
         try {
             if (CommandLineLauncher.cmdArgs.debugMode) {
                 String exp = Utils.getExpressionFromPosition(position);
-                System.out.println(String.format("%s <: %s %s at %s", expected, found, exp ? String.format("on expression '%s'", exp) : "" ,
+                System.out.println(String.format("%s <: %s %s at %s", expected, found,
+                        exp == null ? String.format("on expression '%s'", exp) : "",
                         position.getFile().getName() + ":" + position.getLine()));
             }
             return new SMTEvaluator().verifySubtype(found, expected, context);