message: docs(isRefType): update for current implementation
diff: @@ -8,7 +8,7 @@ title: 'isRefType & isRefTypeArray'
  **Typings:**
  ```ts
  -function isRefType<T, S extends RefType>(doc: Ref<T, S> | undefined, refType: AllowedRefTypes): doc is NonNullable<S>
  +function isRefType<T, S extends RefType>(doc: Ref<T, S> | null | undefined, refType: AllowedRefTypes): doc is NonNullable<S>
  ```
  **Parameters:**
  @@ -31,7 +31,7 @@ class Cat {
  // this example could be smaller, but for demonstation purposes this is a longer version
  public hasPartner(): boolean {
  if (isRefType(this.partner, mongoose.Types.ObjectId)) {
  - // "this.partner" now has the type of "Cat._id"'s RefType (This case ObjectId)
  + // "this.partner" now has the type of "Cat._id"'s RefType (in this case "ObjectId")
  return true;
  } else {
  return false;
  @@ -93,7 +93,7 @@ class Cat {
  // this example could be smaller, but for demonstation purposes this is a longer version
  public areAllKittensExisting(): boolean {
  if (isRefTypeArray(this.kittens, mongoose.Types.ObjectId)) {
  - // "this.kittens" now has the type of "Cat._id"'s RefType (This case ObjectId)
  + // "this.kittens" now has the type of "Cat._id"'s RefType (in this case "ObjectId")
  return true;
  } else {
  return false;
  