Streamreader with multiple files

Hey there,

I can't seem to find any questions/solutions throughout the web that correlate to this particular scenario, so I figured I'd give a breakdown on what I'm trying to achieve using the StreamReader type.

Basically I have 2 files with unbalanced lines counts i.e. data1.txt contains contains 20 lines, whereas data2.txt contains 10, so I'm using StreamReader to first read data from both .txt files, and I was thinking I could use the while (((ts.transaction = t.ReadLine()) !=null)||((ms.master = t.ReadLine()) !=null)) to read the total lines from both files, and then I could continue with applying additional logic to merge my data into a 3rd file afterwards.

However, when I run the following below, I'm running into a "Object reference not set to an instance of an object" likely because of the unbalanced line count? It seems to work when I replace "||" in the while statement with "&&" however I'm unable to print the total number of lines from both files.

At the moment I'm just appending the text to richTextBox1 in order to test my data output for now. I was seeing if there's a better way I can go about using the OR clause, or whether I'm going about this while condition the wrong way?

---

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace credit_card
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        //Read Transaction File
        private void button1_Click(object sender, EventArgs e)
        {
            richTextBox1.Clear();
            StreamReader t = new StreamReader(@"c:\data1.txt");
            StreamReader m = new StreamReader(@"c:\data2.txt");

            transaction_storage ts = new transaction_storage();
            master_storage ms = new master_storage();

            while (((ts.transaction = t.ReadLine()) !=null)||((ms.master = t.ReadLine()) !=null))
            //while ((ts.transaction = t.ReadLine()) != null)
            {
                ms.m_index = Convert.ToInt32(ms.master.Substring(0, 2));

                ts.t_index = Convert.ToInt32(ts.transaction.Substring(0, 2));
                ts.t_name = ts.transaction.Substring(2, 10);
                ts.t_item = ts.transaction.Substring(10, 17);
                ts.t_amount = Convert.ToDouble(ts.transaction.Substring(ts.transaction.Length -7, 7));
                string transaction_data = (ts.t_index.ToString() + " " + ts.t_name + " " + ts.t_item + " " + ts.t_amount + "\n");
                string master_data = (ms.m_index.ToString());

                richTextBox1.AppendText(transaction_data);
                richTextBox1.AppendText(master_data);
            }

            t.Close();
            m.Close();

        }


        class master_storage
        {
            public int m_index;
            public string master;
        }

        class transaction_storage
        {

            public int t_index;
            public string t_name;
            public string t_item;
            public double t_amount;
            public string transaction;
        }

    }
}