title: Is bug ? Optaplanner unable to remove ConstraintMatch
body: <p>I encountered a problem, which is consistent with the problem on this link.
  -&gt; <a href="https://stackoverflow.com/questions/48501563/optaplanner-unable-to-remove-constraintmatch">Optaplanner unable to remove ConstraintMatch</a></p>
  <blockquote>
  <p>Exception:<br />
  org.optaplanner.core.api.score.constraint.ConstraintMatchTotal.removeConstraintMatch</p>
  </blockquote>
  <p>I debugged, and both hashCode and Equals were rewritten, but errors were still reported.</p>
  <p>Rule:</p>
  <pre><code>rule &quot;scheduleFullTimeLimit&quot;
       when
           $shiftList: ArrayList() from collect (
                       StaffAssignment(
                           shiftType != null
                   )
                   )
       then
           scoreHolder.addSoftConstraintMatch(kcontext, -1);
  end
  </code></pre>
  <p>I used collect in my rules.</p>
  <p>Is this a bug?</p>
  <p>Beg your help</p>