code: public synchronized void putInEntryIfNotEmpty() {
  		assert workbenchEntry != null : this;
  		assert acquired : this;
  		assert workbenchEntry.acquired : workbenchEntry;
  		if (! isEmpty()) workbenchEntry.add(this);
  		acquired = false;
  	}
docs: Puts this visit state in its entry, if it not empty.
  
  <p>This method is called only by {@link Workbench#release(VisitState)}.
  Note that the associated entry is <em>not</em> put back on the workbench. Use
  {@link WorkbenchEntry#putOnWorkbenchIfNotEmpty(Workbench)} for that purpose.
  
  <ul>
  <li>Preconditions: {@link #workbenchEntry} &ne; {@code null}, {@link #acquired}.
  <li>Postconditions: not {@link #acquired}.
  </ul>