title: GridGain requirements for a cache key where value is to be used with Sql Queries
body: <p>I am trying to execute a <code>GridCacheQuery</code> created with <code>createSqlQuery()</code> on a cache that I am using a custom Key type for. The problem is that this always gives me back an empty collection, even when there are matching results. </p>
  
  <p>If I repeat the test with a non-custom key type, such as <code>String</code> or <code>Integer</code>, I get the results back that I would expect.</p>
  
  <p>If I repeat the test using a <code>createSqlFieldsQuery()</code> query, this time with the custom key again, I also get the results I would expect!</p>
  
  <p>Is this behaviour expected? I have tested this with 6.5.0-p1, and my custom key type overrides <code>hashCode()</code> and <code>equals()</code>, and even implements <code>Comparable</code>, for what it's worth.</p>