title: Clear HashMap Values While Retaining Keys
body: <p>Is there a way to clear all of the values, while retaining the keys?  </p>
  
  <p>My <code>HashMap</code> is <code>&lt;String,String&gt;</code>, so should I just loop through and replace each <code>value</code> with a <code>null</code>? Is there a better way to do it?</p>