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

@@ -3,6 +3,6 @@ defmodule Pleroma.Repo.Migrations.CopyMutedToMutedNotifications do
   alias Pleroma.User
 
   def change do
-  execute("update users set info = jsonb_set(info, '{muted_notifications}', info->'mutes', true) where local = true")
+  execute("update users set info = safe_jsonb_set(info, '{muted_notifications}', info->'mutes', true) where local = true")
   end
 end