code: public static File getServerConfigDir(String serverName) {
          if (serverName == null) {
              throw new IllegalArgumentException("Parameter serverName can not be 'null'");
          }
          File userDir = Utils.getUserDir();
          if (userDir != null) {
              return new File(new File(userDir, "servers"), serverName);
          }
          return null;
      }
docs: Returns server configuration directory. This directory contains server configuration files
  (bootstrap.properties, server.xml, jvm.options, etc). It correspond to the value of ${server.config.dir}
  variable in server.xml configuration file.
  
  @param serverName server's name
  @return instance of the server configuration directory or 'null' if installation directory
  can't be determined.