code: public static void setAdditionalFields(String spec, GelfMessageAssembler gelfMessageAssembler) {
          if (null != spec) {
              String[] properties = spec.split(MULTI_VALUE_DELIMITTER);
  
              for (String field : properties) {
                  final int index = field.indexOf(EQ);
                  if (-1 == index) {
                      continue;
                  }
                  gelfMessageAssembler.addField(new StaticMessageField(field.substring(0, index), field.substring(index + 1)));
              }
          }
      }
docs: Set the additional (static) fields.
  
  @param spec field=value,field1=value1, ...
  @param gelfMessageAssembler the Gelf message assembler to apply the configuration