Including in a query if a column is null or the column is not null - Is this necessary?

  I think that the Developer  is including if the column is null or the column is not null and don't know if this is necessary to do.
Version 9.2.0.8 - Oralce Database Enterprise Edition.

SELECT * FROM (SELECT dsl_modems.pk_dsl_modem_id, dsl_modems.serial_number, mtm_dsl_modem_2_customer
.fk_dslam_port_id, mtm_dsl_modem_2_customer.fk_customer_id
FROM dsl_modems, mtm_dsl_modem_2_customer  
WHERE      mtm_dsl_modem_2_customer.fk_dsl_modem_id (+)= dsl_modems.pk_dsl_modem_id
AND      dsl_modems.fk_modem_status_id = 'WORKIN'
AND fk_dslam_port_id IS NULL 
AND dsl_modems.brand='ST716g'