I have dumped a clean, no owner backup for Postgres Database with the command
pg_dump sample_database -O -c -U
Later, when I restore the databas
Shorter answer: ignore it.
This module is the part of Postgres that processes the SQL language. The error will often pop up as part of copying a remote database, such as with a 'heroku pg:pull'. It does not overwrite your SQL processor and warns you about that.