protected String getCommandParameterValue(String propertyName) {
    Map<String, String> commandParameters = getCommandParameters();
    return (commandParameters == null) ? null : commandParameters.get(propertyName);
  }
Attempts to safely retrieve a property with the specified name from the this action's relevant
command parameters Map.

@param propertyName a String declaring the name of the item from commandParameters to retrieve
@return the value of the requested property, or null if not found or set
ambari-server/src/main/java/org/apache/ambari/server/serveraction/AbstractServerAction.java