replace Repo.get_by(User, nickname: nickname) with User.get_by_nickname(nickname)

lib/pleroma/web/mastodon_api/mastodon_api_controller.ex

@@ -755,7 +755,7 @@ defmodule Pleroma.Web.MastodonAPI.MastodonAPIController do
   end
 
   def follow(%{assigns: %{user: follower}} = conn, %{"uri" => uri}) do
-    with %User{} = followed <- Repo.get_by(User, nickname: uri),
+    with %User{} = followed <- User.get_by_nickname(uri),
          {:ok, follower, followed, _} <- CommonAPI.follow(follower, followed) do
       conn
       |> put_view(AccountView)

lib/pleroma/web/twitter_api/twitter_api.ex

@@ -227,12 +227,9 @@ defmodule Pleroma.Web.TwitterAPI.TwitterAPI do
         end
 
       %{"screen_name" => nickname} ->
-        case target = Repo.get_by(User, nickname: nickname) do
-          nil ->
-            {:error, "No user with such screen_name"}
-
-          _ ->
-            {:ok, target}
+        case User.get_by_nickname(nickname) do
+          nil -> {:error, "No user with such screen_name"}
+          target -> {:ok, target}
         end
 
       _ ->