title: Postgresql + Django : Not Null Fields Empty Value
body: <p>I know the title doesn't make any sense, but I just want to know how to insert an empty string or '' in a CharField made in Django? As far as I know by default, fields in Django are not nullable. Checking data in PGAdmin, I can see that most of the CharFields have '' as value. I wonder how is this possible? If I run </p>
  
  <pre><code>  cur_p.execute("""
                  INSERT INTO "table"name" (address, school_address, sports ) VALUES ('', '', '')
  </code></pre>
  
  <p>I will get <code>psycopg2.IntegrityError: null value in column "created" violates not-null constraint</code></p>
  
  <p>Also I noticed that some fields have <code>blank=True</code> in them. Doesn't it contradict if you have a not nullable field then you declared <code>blank=True</code>?</p>