Postgresql timestamp update set null

I have a problem with timestamp field in postgresql database its

scheduled_time timestamp without time zone,

And i would like to get posibility to set it to null on update. But its still

ERROR: column "scheduled_time" is of type timestamp without time zone but expression is of type bytea Wskazówka: You will need to rewrite or cast the expression.

I tried to set it null, i tried to set it empty string "" i tried to find solutions at internet, i know that its work when i set it at pgadmin to null, but when i set as a parameter in

 queryString = "UPDATE upload SET additional_info=:additionalInfo, customer_id=:customerId, scheduled_time=:scheduledTime WHERE upload_id=:uploadId"; 
        final Query query = entityManager.createNativeQuery(queryString);   
        query.setParameter("scheduledTime", upload.getScheduledTime());
        more setParameters ....
        query.executeUpdate();

Its still get me that message with type bytea. Can you tell me how to solve that?

I will do it by checking if scheduled is null. When true, i will make

UPDATE upload SET additional_info=:additionalInfo, customer_id=:customerId, scheduled_time= NULL WHERE upload_id=:uploadId

else i will

UPDATE upload SET additional_info=:additionalInfo, customer_id=:customerId, scheduled_time=:scheduledTime WHERE upload_id=:uploadId

couse i didn't find any normal solution.