title: Error on updating nvarchar(max) column from Python
body: <p>I'm updating the output of Google reverse geocoding (which is in JSON format),</p>
  
  <pre><code>cnxn = pyodbc.connect('DRIVER={SQL Server};SERVER=localhost;DATABASE=mydb;UID=test;PWD=abc@123;autocommit=True')
  cursor = cnxn.cursor()
  wp = urllib.request.urlopen("http://maps.googleapis.com/maps/api/geocode/json?latlng=18.5504,73.9412&amp;sensor=false")
  pw = wp.read()
  #print(pw)
  cursor.execute("UPDATE GEOCODE_tbl SET JSON_str = ? WHERE GEOCODE_ID = ?", pw,749904)
  print('Done')
  cnxn.commit()
  </code></pre>
  
  <p>But it gives error</p>
  
  <pre><code>('22018', '[22018] [Microsoft][ODBC SQL Server Driver][SQL Server]Operand type clash: image is incompatible with nvarchar(max) (206) (SQLExecDirectW)')
  </code></pre>
  
  <p>What kind of error is that?
  The JSON_str column has such JSON output, so I'm executing the task for those column whose <code>JSON_str</code> column is NULL.</p>
  
  <p>Does anyone have any idea about it?</p>