Unable to recognize type of Postgres xact advisory locks

[sreekanthgs]

Steps to reproduce

[2] pry(main)> ActiveRecord::Base.connection.select_values("Select pg_advisory_xact_lock(1);")
   (1.5ms)  Select pg_advisory_xact_lock(1);
unknown OID 2278: failed to recognize type of 'pg_advisory_xact_lock'. It will be treated as String.
=> [""]

Expected behavior

Warning should not be thrown. It was working fine in previous versions of active record.

Actual behavior

Warning is issued. Uncertain if the lock is applied, still inspecting.

System configuration

Rails version: 5.1.2
Ruby version: 2.4.1

[sgrif]

pg_advisory_xact_lock has no return value (the type with that OID is void). Use execute instead.

[matthewd]

@sgrif seems like we should probably have a built-in conversion for void to a nil, though?