code: @Override
      public void visitCode(Code obj) {
          try {
              lnTable = obj.getLineNumberTable();
              if (lnTable != null) {
                  state = State.SEEN_NOTHING;
                  invokePC = -1;
                  returnType = null;
                  super.visitCode(obj);
              }
          } finally {
              lnTable = null;
          }
      }
docs: overrides the interface to collect the line number table, and reset state
  
  @param obj
  the content object of the currently parsed code