Fix a migration wiping user info of users that don't have any mutes

And introduce safe_jsonb_set

priv/repo/migrations/20190711042021_create_safe_jsonb_set.exs

@@ -0,0 +1,22 @@
+defmodule Pleroma.Repo.Migrations.CreateSafeJsonbSet do
+  use Ecto.Migration
+  alias Pleroma.User
+
+  def change do
+    execute("""
+    create or replace function safe_jsonb_set(target jsonb, path text[], new_value jsonb, create_missing boolean default true) returns jsonb as $$
+    declare
+      result jsonb;
+    begin
+      result := jsonb_set(target, path, coalesce(new_value, 'null'::jsonb), create_missing);
+      if result is NULL then
+        raise 'jsonb_set tried to wipe the object, please report this incindent to Pleroma bug tracker. https://git.pleroma.social/pleroma/pleroma/issues/new';
+        return target;
+      else
+        return result;
+      end if;
+    end;
+    $$ language plpgsql;
+    """)
+  end
+end

priv/repo/migrations/20190711042024_copy_muted_to_muted_notifications.exs

@@ -4,7 +4,7 @@ defmodule Pleroma.Repo.Migrations.CopyMutedToMutedNotifications do
 
   def change do
     execute(
-      "update users set info = jsonb_set(info, '{muted_notifications}', info->'mutes', true) where local = true"
+      "update users set info = safe_jsonb_set(info, '{muted_notifications}', info->'mutes', true) where local = true"
     )
   end
 end