Oracle Database 12c -- ORA-01549: tablespace not empty, use INCLUDING CONTENTS option

Problem

While dropping a tablespace, you receive the ORA-01549: tablespace not empty, use INCLUDING CONTENTS option error. 

At the same time, you check for objects in the tablespace with DBA_SEGMENTS, and see no objects.

Solution

There might be objects assigned to the tablespace with DEFERRED SEGMENT CREATION option. In this case, segments for objects have not yet been created, but still bound to the tablespace

To identify those objects use the query below:

select * from dba_objects 
where object_id in (
    select object_id from sys.sys_objects 
    where ts_number = (
        select ts# from v$tablespace where name = '<tbs_name>'
    )
);