void invalidateJson() {
    if (executionCommand == null) {
      throw new RuntimeException("Invalid Wrapper object");
    }
    jsonExecutionCommand = null;
  }
Gets the type of command by deserializing the JSON and invoking
{@link ExecutionCommand#getCommandType()}.

@return
ambari-server/src/main/java/org/apache/ambari/server/actionmanager/ExecutionCommandWrapper.java