Why cursor's resultset wrapper is null ?

[AlwaysNoobCoder]

Cursor<User> streamByExample(UserExample example);

<select id="streamByExample" parameterType="com.wxt.itps.services.pub.models.UserExample" resultMap="BaseResultMap">
    <if test="distinct">
      distinct
    </if>
    <if test="filter != null">
      where ${_parameter.getConditions()}
    </if>
    <if test="orders != null and orders.size() gt 0">
      order by ${_parameter.getOrderBy('')}
    </if>
  </select>

when call it:

Caused by: java.lang.NullPointerException: Cannot invoke "org.apache.ibatis.executor.resultset.ResultSetWrapper.getResultSet()" because "this.rsw" is null
	at org.apache.ibatis.cursor.defaults.DefaultCursor.close(DefaultCursor.java:112)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.closeCursors(DefaultSqlSession.java:275)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.close(DefaultSqlSession.java:264)
	at org.mybatis.spring.SqlSessionUtils.closeSqlSession(SqlSessionUtils.java:200)
	at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:447)
	at jdk.proxy2/jdk.proxy2.$Proxy99.selectCursor(Unknown Source)
	at org.mybatis.spring.SqlSessionTemplate.selectCursor(SqlSessionTemplate.java:200)
	at org.apache.ibatis.binding.MapperMethod.executeForCursor(MapperMethod.java:166)
	at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:84)
	at org.apache.ibatis.binding.MapperProxy$PlainMethodInvoker.invoke(MapperProxy.java:141)
	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:86)
	at jdk.proxy3/jdk.proxy3.$Proxy121.streamByExample(Unknown Source)
	... 31 more

any hint on this ?

[AlwaysNoobCoder]

the sql is empty ... sorry.