output: #fixed code
                                  private void atPlusPlus(int token, ASTree oprand, Expr expr)
          throws CompileError
      {
          boolean isPost = oprand == null;        // ++i or i++?
          if (isPost)
              oprand = expr.oprand2();
  
          if (oprand instanceof Variable) {
              Declarator d = ((Variable)oprand).getDeclarator();
              exprType = d.getType();
              arrayDim = d.getArrayDim();
          }
          else {
              if (oprand instanceof Expr) {
                  Expr e = (Expr)oprand;
                  if (e.getOperator() == ARRAY) {
                      atArrayRead(e.oprand1(), e.oprand2());
                      // arrayDim should be 0.
                      int t = exprType;
                      if (t == INT || t == BYTE || t == CHAR || t == SHORT)
                          exprType = INT;
  
                      return;
                  }
              }
  
              atFieldPlusPlus(oprand);
          }
      }
input: #vulnerable code 
                                  private void atPlusPlus(int token, ASTree oprand, Expr expr)
          throws CompileError
      {
          boolean isPost = oprand == null;        // ++i or i++?
          if (isPost)
              oprand = expr.oprand2();
  
          if (oprand instanceof Variable) {
              Declarator d = ((Variable)oprand).getDeclarator();
              exprType = d.getType();
              arrayDim = d.getArrayDim();
          }
          else {
              if (oprand instanceof Expr) {
                  Expr e = (Expr)oprand;
                  if (e.getOperator() == ARRAY) {
                      atArrayRead(expr.oprand1(), expr.oprand2());
                      // arrayDim should be 0.
                      int t = exprType;
                      if (t == INT || t == BYTE || t == CHAR || t == SHORT)
                          exprType = INT;
  
                      return;
                  }
              }
  
              atFieldPlusPlus(oprand);
          }
      } 
                              #location 17 
                              #vulnerability type NULL_DEREFERENCE