code: public static void setAdditionalFieldTypes(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) {
                      gelfMessageAssembler.setAdditionalFieldType(field.substring(0, index), field.substring(index + 1));
                  }
              }
          }
      }
docs: Set the additional field types.
  
  @param spec field=String,field1=Double, ... See {@link GelfMessage} for supported types.
  @param gelfMessageAssembler the Gelf message assembler to apply the configuration