Fix NPE When Invoking Methods on Object Fields

Author: rcosta358

liquidjava-verifier/src/main/java/liquidjava/processor/refinement_checker/object_checkers/AuxStateHandler.java

@@ -594,6 +594,8 @@ public static String prepareInvocationTarget(TypeChecker tc, CtElement target2,
             // v--------- field read
             // means invocation is in a form of `t.method(args)`
             String name = v.getVariable().getSimpleName();
+            if (v instanceof CtFieldRead<?>)
+                name = String.format(Formats.THIS, name);
             Optional<VariableInstance> invocationCallee = tc.getContext().getLastVariableInstance(name);
             if (invocationCallee.isPresent()) {
                 invocation.putMetadata(Keys.TARGET, invocationCallee.get());