message: refactor: return is better when inject has no value
diff: @@ -334,6 +334,7 @@ function validatePropObject (
  */
  function normalizeInject (options: Object, vm: ?Component) {
  const inject = options.inject
  + if (!inject) return
  const normalized = options.inject = {}
  if (Array.isArray(inject)) {
  for (let i = 0; i < inject.length; i++) {
  @@ -346,7 +347,7 @@ function normalizeInject (options: Object, vm: ?Component) {
  ? extend({ from: key }, val)
  : { from: val }
  }
  - } else if (process.env.NODE_ENV !== 'production' && inject) {
  + } else if (process.env.NODE_ENV !== 'production') {
  warn(
  `Invalid value for option "inject": expected an Array or an Object, ` +
  `but got ${toRawType(inject)}.`,
  