message: fix: keep empty selected dicts
diff: @@ -151,6 +151,9 @@ export function mergeConfig (oldConfig: AppConfig, baseConfig?: AppConfig): AppC
  function mergeSelectedDicts (path: string): void {
  const selected = get(oldConfig, [path, 'selected'])
  if (Array.isArray(selected)) {
  + if (selected.length === 0) {
  + set(base, [path, 'selected'], [])
  + } else {
  const allDict = get(base, [path, 'all'])
  const arr = selected.filter(id => allDict[id])
  if (arr.length > 0) {
  @@ -158,6 +161,7 @@ export function mergeConfig (oldConfig: AppConfig, baseConfig?: AppConfig): AppC
  }
  }
  }
  + }
  function mergeNumber (path: string): void {
  return merge(path, isNumber)
  