how to pass NULL to parameter map in iBatis

Question

I am trying to pass null to a parameter map but I keep getting error saying:

--- Check the parameter mapping for the 'something' property. 

How I cam calling code:

HashMap myMap = new HashMap ()

myMap.put("something", null)

getSqlMapClientTemplate().queryForList("list_of_sps.getByLastNameExactMatch", myMap );

My Mappings:

<procedure id="getByLastNameExactMatch" parameterMap="getByLastNameExactMatchCall">{call search_by_exact_lname (?,?) }</procedure>

<parameterMap id="getByLastNameExactMatchCall" class="map">
  <parameter property="something" jdbcType="String" javaType="java.lang.String" mode="IN"/>
  <parameter property="Result0" jdbcType="ORACLECURSOR" javaType="java.sql.ResultSet" mode="OUT" resultMap="myResultMap"/>
</parameterMap>

What do I need to do in order to be able to pass NULL to the stored procedure?

Thanks