null tablespace?

I have not defined my default tablespace:

show default_tablespace ;
 default_tablespace
--------------------


However, I have tables with null tablespaces values in pg_tables:

pg_dw=# select * from pg_tables where tablename = 'source_prev';
 schemaname |       tablename       | tableowner | tablespace | hasindexes | hasrules | hastriggers
------------+-----------------------+------------+------------+------------+----------+-------------
 support    | source_prev           | jspool     |            | t          | f        | f


We have defined out search_path correctly, so what tablespace is this table stored in?

Thanks!