title: PostgreSQL: how to insert null value to uuid
body: <p>Need to insert null value to field with <code>uuid</code> type without <strong>NOT NULL</strong> specification (not primary key).</p>
  
  <p>When I try insert '', this return:</p>
  
  <pre><code>ERROR:  invalid input syntax for uuid: ""
  </code></pre>
  
  <p>When I try insert null, this return:</p>
  
  <pre><code>ERROR:  null value in column "uuid" violates not-null constraint
  </code></pre>
  
  <p>How to do it?</p>
  
  <p>psql 9.3.5</p>
  
  <p>SQL:</p>
  
  <pre><code>INSERT INTO inv_location (address_id)
  VALUES (null)
  </code></pre>