code: public MethodState getSaved(int idx) {
          if (idx < 0) {
              throw new IllegalArgumentException();
          }
  
          MethodState state = firstPointer;
          for (int i = 0; i < idx; i++) {
              state = state.getNext();
              if (state == null) {
                 throw new IllegalArgumentException();
              }
          }
          return state;
      }
docs: Do not use -- for internal use only. For testing.
  @param idx n/a
  @return n/a