code: public static OptionDefinition get(String id, InstallOptions options) {
          String label = _PROPS.getProperty(id + ".label");
          String description = _PROPS.getProperty(id + ".description");
          String[] validValues = getArray(id + ".validValues");
          String defaultValue = _PROPS.getProperty(id + ".defaultValue");
  
          // If label, description, validValues and defaultValue are all null,
          // assume that no definition for the id exists.
          //if (label == null && description == null && validValues == null &&
          // 		defaultValue == null) {
          // 	return null;
          //}
  
          // Use the environment variable FEDORA_HOME as the default, if defined
          if (id.equals(InstallOptions.FEDORA_HOME)) {
              String eFH = System.getenv("FEDORA_HOME");
              if (eFH != null && eFH.length() != 0) {
                  defaultValue = eFH;
              }
          }
  
          // Use CATALINA_HOME as the default, if defined.
          if (id.equals(InstallOptions.TOMCAT_HOME)) {
              String eCH = System.getenv("CATALINA_HOME");
              if (eCH != null && eCH.length() != 0) {
                  defaultValue = eCH;
              } else if (options.getValue(InstallOptions.SERVLET_ENGINE)
                      .equals(InstallOptions.INCLUDED)) {
                  defaultValue =
                          options.getValue(InstallOptions.FEDORA_HOME)
                                  + File.separator + "tomcat";
              }
          }
  
          return new OptionDefinition(id,
                                      label,
                                      description,
                                      validValues,
                                      defaultValue,
                                      options);
      }
docs: Get the definition of the identified option, or <code>null</code> if no
  such definition exists.