title: Insert null into Datetime field
body: <p>I have a DATETIME column(Default is NULL) in MySQL and trying to insert Empty or NULL value. But I am getting "Incorrect datetime value: '' " error message. 
  If I insert 'NULL' then I am getting "Incorrect datetime value: 'NULL'" error message. How can I insert a blank or NULL value in this column? Thank you for any suggestions.</p>
  
  <p>Here is the code.</p>
  
  <pre><code>        if (empty($_POST["date_field"]))
          {      
            $Date1 = 'NULL';
          }
          else
          {
             $Date1 = strtotime($_POST["date_field"]);
             $Date1 = date("Y-m-d H:i:s", $Date1);
          }
  
     INSERT INTO Table1(date_field) VALUES('" .$Date1. "');
  </code></pre>