protected static String getCommandParameterValue(Map<String, String> commandParameters, String propertyName) {
    return ((commandParameters == null) || (propertyName == null)) ? null : commandParameters.get(propertyName);
  }
Given a (command parameter) Map and a property name, attempts to safely retrieve the requested
data.

@param commandParameters a Map containing the dictionary of data to interrogate
@param propertyName      a String declaring the name of the item from commandParameters to retrieve
@return a String or null, depending on the property value and if it existed in commandParameters
ambari-server/src/main/java/org/apache/ambari/server/serveraction/kerberos/KerberosServerAction.java