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!