Type conversion from DAO to controller

I am stuck in the below issue. I tried to trace out but couldn't. Can you guys please do me a favour to solve this issue.

In my controller :

Long id = '1425652';
Collection<Long> propIds =  extealTaxManager.getPropertyIdsByTaxId(id); // I have an issue here
Map<Long, Long> propIdToOnegIdMap = extealTaxManager.mapPropertiesToOnegIds(propIds);

In my DaoImpl :

public Collection<Long> getPropertyIdsByTaxId(Long extealTaxId){
        SQLQuery query = currentSession().createSQLQuery("select b.OMH_PROPERTY_ID from OMH.OMH_EXTERNAL_TAX a , OMH.OMH_EXTERNAL_TAX_PROP_XREF bn" +
                "where a.OMH_EXTERNAL_TAX_ID=b.OMH_EXTERNAL_TAX_ID and a.OMH_EXTERNAL_TAX_ID= :extealTaxId ");
        query.setParameter("extealTaxId", extealTaxId);
        List<Long> result = query.list();
        retu result;
}

Here, b.OMH_PROPERTY_ID is long type. There are more than 1000 records in DB for each extealTaxId we pass.

But there is a type mismatch when I am retuing from DAO to Controller. I need propIds Collection only.

Thanks in advance.