org.postgresql.util.PSQLException: The column name plan_id was not found in this ResultSet.

    <hibernate-mapping>
   <database-object>
      <create>
    CREATE OR REPLACE FUNCTION copy_plan(p_plan_id bigint, p_plan_for_year varchar, p_copy_pp boolean)
    RETURNS REFCURSOR
    AS $$
   DECLARE
      result REFCURSOR;
      // some more declarations
   BEGIN
      // a lot of logic which works fine

      OPEN result FOR
      SELECT  plans.plan_id as plan_id,
            plans.plan_for_year as plan_for_year,
            plans.plan_plan_id as plan_plan_id,
            plans.plan_f_type as plan_f_type,
            plans.plan_enabled as plan_enabled
      FROM rgt_plans plans WHERE plans.plan_id = v_plan_id;
         
      RETURN result;

   END;
    $$ LANGUAGE PLPGSQL
      </create>
      <drop>DROP FUNCTION copy_plan</drop>
   </database-object>
</hibernate-mapping>

    @Entity
    @Table(name = "rgt_plans")
    @NamedNativeQueries({ @NamedNativeQuery(name = "copyPlan", query = "select copy_plan(:planId, :newYear, :copy)", resultClass=Plan.class) })
    public class Plan implements Serializable {

   private static final long serialVersionUID = -8448579977833577641L;

   @Id
   @GeneratedValue(generator = "IdGenerator", strategy = GenerationType.TABLE)
   @TableGenerator(name = "IdGenerator", pkColumnValue = "rgt_plans", table = "Sequence_Table", allocationSize = 1)
   @Column(name = "plan_id", columnDefinition = "int4")
   private Long id;

   @Column(name = "plan_for_year")
   @NotNull
   private String forYear;

   @Column(name = "plan_plan_id")
   @Basic
   private Long plan_id;

   @Column(name = "plan_f_type", length = 1)
   @Basic
   @NotNull
   private String type;

   @Column(name = "plan_enabled")
   @Basic
   @NotNull
   private Boolean enabled;

   // getters, setters, equals, hashcode

    }

    public List<Plan> copyPlan(Long currentPlanId, String newYear, Boolean copy) {
      return this.getHibernateTemplate()
            .findByNamedQueryAndNamedParam("copyPlan",
                  new String[] { "planId", "newYear", "copy" },
                  new Object[] { currentPlanId, newYear, copy });

   }