title: How to store empty value as an Integerfield
body: <p>I've seen all the similar threads, read the docs, and tried many combinations to store an empty value as <code>IntegerField</code> in db and failed every single time. </p>
  
  <p>I am using MySQL. </p>
  
  <p>My <code>models.py</code> defines an <code>age=models.IntegerField()</code> field. I populate db from csv file, and some cells have no value. Django docs says:</p>
  
  <pre><code>Field.null
  
  If True, Django will store empty values as NULL in the database. Default is False.
  Note that empty string values will always get stored as empty strings, not as NULL. 
  </code></pre>
  
  <p>Since I am working with <code>IntegerField</code> I want an empty string (an empty cell from the csv) to be stored as <code>NULL</code> in db. Therefore, I (think) have to add <code>null=True</code> to the <code>age</code> field. Actually, I've tried more than this:</p>
  
  <pre><code>age=models.IntegerField()
  age=models.IntegerField(null=True)
  age=models.IntegerField(null=True, blank=True)
  age=models.IntegerField(null=True, blank=True, default=None)
  </code></pre>
  
  <p>and every time I am inserting an empty string to a db I got </p>
  
  <pre><code>ValueError: invalid literal for int() with base 10: ''
  </code></pre>
  
  <p>Any guess what else can I do?</p>