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