code: function toNumberOrUndefined(n) {
      if (n === null || n === undefined) { return undefined; }
      if (validation.isObject(n) || validation.isArray(n)) { return undefined; }
      if (typeof n === 'boolean' || (typeof n === 'string' && n.length < 1)) { return undefined; }
      return isNaN(+n) ? undefined : +n;
  }
docs: Receives anything and tries to convert into a number. If it is not possible to be
  converted into a number (object, array, null, undefined), or it is NaN, it gets
  converted into undefined.
  
  @param {*} n
  @returns {Number|undefined}