code: function CommandHandler (meta, cmdHndlFn) {
    DefaultCommandHandler.call(this, meta);
  
    console.log('Is your use case not solvable without a custom command handling? Sagas? Micro-Services?');
  
    meta = meta || {};
  
    this.version = meta.version || 0;
  
    if (!cmdHndlFn || !_.isFunction(cmdHndlFn)) {
      var err = new Error('CommandHandler function not injected!');
      debug(err);
      throw err;
    }
  
    this.cmdHndlFn = cmdHndlFn;
  }
docs: CommandHandler constructor
  @param {Object}   meta      Meta infos like: { name: 'name', version: 1 }
  @param {Function} cmdHndlFn Function handle
  `function(aggId, cmd, commandHandler, callback){}`
  @constructor