How to generate is null not =null when using Hibernate

Dear All,When i using HQL(SELECT t FROM TBsraFlight t WHERE t.flightNum=:fltnumber AND t.status=‘Flt_Processing’) and the flightnumber is a java bean contains suffix may be null,but the hibernate generate these SQL-Hibernate: select as id1_0_, tbsrafligh0_.create_date_time as create_d2_0_, tbsrafligh0_.endtime as endtime3_0_, tbsrafligh0_.airline as airline4_0_, tbsrafligh0_.num as num5_0_, tbsrafligh0_.suffix as suffix6_0_, tbsrafligh0_.operator as operator7_0_, tbsrafligh0_.qb_id as qb_id13_0_, tbsrafligh0_.remark1 as remark8_0_, tbsrafligh0_.remark2 as remark9_0_, tbsrafligh0_.schedules as schedul10_0_, tbsrafligh0_.starttime as startti11_0_, tbsrafligh0_.flight_status as flight_12_0_ from t_bsra_flight tbsrafligh0_ where tbsrafligh0_.airline=? and tbsrafligh0_.num=? and tbsrafligh0_.suffix=? and tbsrafligh0_.flight_status=‘Flt_Processing’,i want to know how to make suffix=null change to suffix is null?