title: Data truncated for column 'x' when updating to NULL
body: <p>I have a MySQL table containing a column named free_delivery_treshold of type float, NOT NULL <strong>unchecked</strong>.
  If I insert data omitting this column, the default value (NULL) is inserted.
  However, if I <strong>update</strong> its value to <code>NULL</code>, empty string or <code>\N</code> I get a </p>
  
  <blockquote>
    <p>WARN_DATA_TRUNCATED: Data truncated for column 'free_delivery_treshold' at row 1</p>
  </blockquote>
  
  <p>error.</p>
  
  <p>How do I update the value of this column to NULL ?</p>