private PreconfigureServiceType getPreconfigureServiceType(Map<String, Map<String, String>> configurations) {
    String preconfigureServices = getValueFromConfiguration(configurations, KERBEROS_ENV, PRECONFIGURE_SERVICES);

    PreconfigureServiceType preconfigureServiceType = null;
    if (!StringUtils.isEmpty(preconfigureServices)) {
      try {
        preconfigureServiceType = PreconfigureServiceType.valueOf(preconfigureServices.toUpperCase());
      } catch (Throwable t) {
        preconfigureServiceType = PreconfigureServiceType.DEFAULT;
      }
    }

    return (preconfigureServiceType == null) ? PreconfigureServiceType.DEFAULT : preconfigureServiceType;
  }
Safely retrieves the <code>preconfigure_services</code> property of the <code>kerberos-env</code> configuration.

@param configurations the existing configurations for the cluster
@return the requested value or null if the configuration does not exist
@see #getValueFromConfiguration(Map, String, String)
ambari-server/src/main/java/org/apache/ambari/server/serveraction/upgrades/PreconfigureKerberosAction.java