title: inserting null dates in MySql with pymysql
body: <p>I am trying to insert dates into a MySql database using pymysql and parameters. Some of the rows have a date field but for some others that particular date field is missing. The empty rows give an error of the type "pymysql.err.InternalError: (1292, "Incorrect date value:". Below is a piece of code that reproduces the error:</p>
  
  <pre><code>import pymysql
  db=pymysql.connect("localhost","testuser","test1234","TESTDB")
  cursor = db.cursor()
  cursor.execute("SELECT VERSION()")
  data = cursor.fetchone()
  print ("Database version : %s " % data)
  
  query = "DROP TABLE IF EXISTS birthdays"
  cursor.execute(query)
  
  query="CREATE TABLE birthdays(id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,\
  name VARCHAR(20),\
  birthday DATE NULL DEFAULT NULL)"
  cursor.execute(query)
  db.commit()
  
  birthdays={'David':'2014-05-22','Larry':'014-05-22', 'Barry':''}
  
  for k,v in birthdays.items():
      print(k,v)
      query="INSERT INTO birthdays (name,birthday) VALUES ('%s','%s')"%(k,v)
      cursor.execute(query)
      db.commit()
  
  db.close()
  </code></pre>
  
  <p>The problem is with Barry and its empty date. I have tried setting Barry's date to None but it is not working. If I set it up to "NULL" and remove the quotes from the date parameter (('%s',%s) instead of ('%s','%s')) it works for Barry but note for the others.</p>
  
  <p>thank you very much in advance,</p>
  
  <p>Gabriel Vidal</p>