title: adding a key to HashMap without the value?
body: <p>Is there a way to add a key to a HashMap without also adding a value? I know it seems strange, but I have a <code>HashMap&lt;String, ArrayList&lt;Object&gt;&gt;</code> amd I want to first be able to create keys as needed and then check if a certain key exists and, if so, put the appropriate value, namely the <code>ArrayList&lt;Object&gt;</code></p>
  
  <p>Was that confusing enough?</p>