code: public void setDeliveryMode(Integer deliveryMode) {
          if (deliveryMode == null) {
              _properties.remove(AMQP_PROP_DELIVERY_MODE);
              return;
          }
          
          // Perhaps, we could do an enum for deliveryMode. But, it will require
          // some major changes in encoding and decoding and we don't have much
          // time to do it across all the clients.
          int value = deliveryMode.intValue();
          if ((value != 1) && (value != 2)) {
              String s = "AMQP 0-9-1 spec mandates 'deliveryMode' value to be " +
                         "either 1(for non-persistent) or 2(for persistent)";
              throw new IllegalStateException(s);
          }
          
          _properties.put(AMQP_PROP_DELIVERY_MODE, deliveryMode);
      }
docs: Sets the value of "deliveryMode" property.  If a null value is passed
  in, it indicates that the property is not set.
  
  @param  deliveryMode    value of "deliveryMode" property