code: @Override
      public void sawOpcode(int seen) {
          if (seen == Const.PUTFIELD) {
              OpcodeStack stack = getStack();
              if (stack.getStackDepth() > 0) {
                  int reg = stack.getStackItem(0).getRegisterNumber();
                  if ((reg >= 0) && (reg < firstLocalRegister)) {
                      clearSpecialField(getNameConstantOperand());
                  }
              }
          }
          super.sawOpcode(seen);
      }
docs: overrides the visitor to look for PUTFIELDS of collections
  
  @param seen
  the currently parsed opcode