docs: public ValueType getTopValue() throws DataflowAnalysisException {
          if (!isValid()) {
              throw new DataflowAnalysisException("accessing top or bottom frame");
          }
          assert slotList.size() >= numLocals;
          if (slotList.size() == numLocals) {
              throw new DataflowAnalysisException("operand stack is empty");
          }
          return slotList.get(slotList.size() - 1);
      }