code: function serializerKey(message, buffer, key, length, position, cb) {
  
      position.value -= length;
  
      if (isNaN(key)) {
          cb(new Error(`[Serializer] MID[${message.mid}] key invalid [${key}]`));
          return false;
      }
  
      buffer.write(padLeft(key, length), position.value, encoding);
  
      return true;
  }
docs: @description This method performs the serialization of key, the value to be serialized in [buffer]
  comes from [key] on [position.value] with length [length].
  The [key] must be a Number.
  
  The [cb] function is called in cases of error, sending the error as parameter.
  The return of this function is boolean, true: the process without errors or false: the process with an error.
  
  @param {object} message
  @param {buffer} buffer
  @param {number} key
  @param {number} length
  @param {object} position
  @param {Function} cb
  @returns {boolean}