Lexical Parameter Validation in After Parameter Trigger In Report Builder

if :P_CATG_FROM is  null and :P_CATG_TO is  null  then

                :LP_CATEGORY  :=  'and  1=1 ';

    elsif :P_CATG_FROM is not null and :P_CATG_TO is null then

                :LP_CATEGORY := 'and mc.CATEGORY_CONCAT_SEGS >= :P_CATG_FROM';

    elsif :P_CATG_FROM is null and :P_CATG_TO is not null then

                :LP_CATEGORY := 'and mc.CATEGORY_CONCAT_SEGS <= :P_CATG_TO';

    else

                :LP_CATEGORY  := 'and mc.CATEGORY_CONCAT_SEGS BETWEEN :P_CATG_FROM AND  :P_CATG_TO';   

                end if;