title: Set "NULL" in Empty cells in CsvReader
body: <p>Here is my code:</p>
  
  <pre><code>using (System.Net.WebResponse tmpRes = tmpReq.GetResponse())
  {
      using (System.IO.Stream tmpStream = tmpRes.GetResponseStream())
      {
          using (System.IO.TextReader tmpReader = new System.IO.StreamReader(tmpStream))
          {
              string fileContents = tmpReader.ReadToEnd();
              for (int i = 0; i &lt; fileContents.Length; i++)
              {
                  if (fileContents[i] == "")
                  {
                      fileContents[i] = "null";
                  }
              }
              using (Stream s = GenerateStreamFromString(fileContents))
              {}
         }
      }
  } 
  </code></pre>
  
  <p>this shows error 'string' to 'char' convert implicitly. Is there any other way to set <strong>"NULL"</strong> in empty fields in CSVReader </p>