code: @Override
      public void visitClassContext(ClassContext classContext) {
          try {
              refClasses = new HashSet<>();
              refClasses.add(classContext.getJavaClass().getClassName());
              state = State.COLLECT;
              super.visitClassContext(classContext);
              state = State.SEEN_NOTHING;
              super.visitClassContext(classContext);
          } finally {
              refClasses = null;
          }
      }
docs: overrides the visitor to collect all class references
  
  @param classContext
  the class context of the currently visited class