protected static String getDefaultRealm(Map<String, String> commandParameters) {
    return getCommandParameterValue(commandParameters, DEFAULT_REALM);
  }
Given a (command parameter) Map, attempts to safely retrieve the "default_realm" property.

@param commandParameters a Map containing the dictionary of data to interrogate
@return a String indicating the default realm or null (if not found or set)
ambari-server/src/main/java/org/apache/ambari/server/serveraction/kerberos/KerberosServerAction.java