keyErrorMessage(key, genericKey = MongoObject.makeKeyGeneric(key)) {
    if (Object.prototype.hasOwnProperty.call(this._deps, genericKey)) this._deps[genericKey].depend();

    const errorObj = this.getErrorForKey(key, genericKey);
    if (!errorObj) return '';

    return this._simpleSchema.messageForError(errorObj);
  }
@param key
@param genericKey
@return {string|*}