UserStore migration (#15563)

* Migration completed

* Fix tests

* Fix tests

* Fix tests

* Suggestions

* Trigger CI

* Suggestions

* Merge with master

* Trigger CI

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Agniva De Sarker <agnivade@yahoo.co.in>

app/post.go

@@ -53,9 +53,15 @@ func (a *App) CreatePostAsUser(post *model.Post, currentSessionId string, setOnl
 		}
 
 		if err.Id == "api.post.create_post.town_square_read_only" {
-			user, userErr := a.Srv().Store.User().Get(post.UserId)
-			if userErr != nil {
-				return nil, userErr
+			user, nErr := a.Srv().Store.User().Get(post.UserId)
+			if nErr != nil {
+				var nfErr *store.ErrNotFound
+				switch {
+				case errors.As(nErr, &nfErr):
+					return nil, model.NewAppError("CreatePostAsUser", MISSING_ACCOUNT_ERROR, nil, nfErr.Error(), http.StatusNotFound)
+				default:
+					return nil, model.NewAppError("CreatePostAsUser", "app.user.get.app_error", nil, nErr.Error(), http.StatusInternalServerError)
+				}
 			}
 
 			T := utils.GetUserTranslations(user.Locale)
@@ -185,9 +191,15 @@ func (a *App) CreatePost(post *model.Post, channel *model.Channel, triggerWebhoo
 		}()
 	}
 
-	user, err := a.Srv().Store.User().Get(post.UserId)
-	if err != nil {
-		return nil, err
+	user, nErr := a.Srv().Store.User().Get(post.UserId)
+	if nErr != nil {
+		var nfErr *store.ErrNotFound
+		switch {
+		case errors.As(nErr, &nfErr):
+			return nil, model.NewAppError("CreatePost", MISSING_ACCOUNT_ERROR, nil, nfErr.Error(), http.StatusNotFound)
+		default:
+			return nil, model.NewAppError("CreatePost", "app.user.get.app_error", nil, nErr.Error(), http.StatusInternalServerError)
+		}
 	}
 
 	if user.IsBot {