private String getValueFromConfiguration(Map<String, Map<String, String>> configurations, String configType, String propertyName) {
    String value = null;

    if (configurations != null) {
      Map<String, String> kerberosEnv = configurations.get(configType);

      if (kerberosEnv != null) {
        value = kerberosEnv.get(propertyName);
      }
    }

    return value;
  }
Safely retrieves the specified property from the specified configuration type from a map of
configurations.

@param configurations the existing configurations for the cluster
@return the requested value or null if the configuration does not exist
ambari-server/src/main/java/org/apache/ambari/server/serveraction/upgrades/PreconfigureKerberosAction.java