code: function cloneField (v) {
    if (v === null || v === undefined) {
      return v
    } if (Array.isArray(v)) {
      return v.map(cloneField)
    } else if (typeof v === 'object') {
      if ('saveAsJSON' in v) {
        return v.saveAsJSON()
      }
      return Object.assign({}, v)
    }
    return v
  }
docs: Clone a field of a filter (array, object or any primary type)
  @param  {*} v - Value to clone
  @return {*} Cloned value