code: public void setCorrelationId(String correlationId) {
          if (correlationId == null) {
              _properties.remove(AMQP_PROP_CORRELATION_ID);
              return;
          }
          
          _properties.put(AMQP_PROP_CORRELATION_ID, correlationId);
      }
docs: Sets the value of "correlationId" property.  If a null value is passed
  in, it indicates that the property is not set.
  
  @param  correlationId    value of "correlationId" property