code: public String toYaml() throws IOException {
      YAMLMapper mapper = new YAMLMapper();
      mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
      mapper.configure(YAMLGenerator.Feature.ALWAYS_QUOTE_NUMBERS_AS_STRINGS, false);
      mapper.configure(YAMLGenerator.Feature.MINIMIZE_QUOTES, true);
      return "#%RAML 1.0\n" + mapper.writer().withDefaultPrettyPrinter().writeValueAsString(this);
    }
docs: Convert this RAML object to Yaml.
  
  @return Yaml string.
  @throws IOException If something goes wrong.