title: Hibernate mapping a composite key with null values
body: <p>With Hibernate, can you create a composite ID where one of the columns you are mapping to the ID can have null values?</p>
  
  <p>This is to deal with a legacy table that has a unique key which can have null values but no primary key.</p>
  
  <p>I realise that I could just add a new primary key column to the table, but I'm wondering if there's any way to avoid doing this.</p>