How to get an already existing entity root in a JPA criteria query

QueryEntitiesHelper.java

import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Root;
import java.util.Iterator;
import java.util.Set;

/**
 * Created by qlehenaff on 12/10/15.
 */
public class QueryEntitiesHelper<R> {

    public Root<R> getExistingRoot(CriteriaQuery<?> query, Class<R> clazz) {
        Root<R> root = null;
        final Set<Root<?>> roots = query.getRoots();
        if (!roots.isEmpty()) {
            final Iterator<Root<?>> iterator = roots.iterator();
            while (iterator.hasNext()) {
                final Root<?> next = iterator.next();
                if (next.getModel().getName().equals(clazz.getSimpleName())) {
                    root = (Root<R>) next;
                    break;
                }
            }
            if(root == null) {
                root = query.from(clazz);
            }
        } else {
            root = query.from(clazz);
        }
        return root;
    }
}