function normalizeNamespace (fn) {
  return (namespace, map) => {
    if (typeof namespace !== 'string') {
      map = namespace
      namespace = ''
    } else if (namespace.charAt(namespace.length - 1) !== '/') {
      namespace += '/'
    }
    return fn(namespace, map)
  }
}
Return a function expect two param contains namespace and map. it will normalize the namespace and then the param's function will handle the new namespace and the map.
@param {Function} fn
@return {Function}