Test with PostgreSQL warning

i’m new to Hanami (and Ruby also), i post here for an issue, i followed the guide (bookshelf exemple) but using PostgreSQL but when i run the test for the first page i had this warning ( warning: constant Sequel::Postgres::PGArray::EMPTY_BRACKET is deprecated).
when i run the server, the app seem to work perfectly but i still have the same warning
i don’t know if this is an issue or if i failed somewhere, should i worry about that?
i used:
-pg gem : 0.21.0
-PostgreSQL database: 9.6.3
-Sequel gem: 4.49.0
Thank you.