How to solve ORA-14323: cannot add partition when DEFAULT partition exists

You have a partitioned table with an overflow partition, and you try to add another partition to it:

ALTER TABLE RECEIVED_DOCUMENTS 
ADD PARTITION EES_COUNTRIES VALUES('NORWAY','ICELAND')

Result:

ERROR at line 1:
ORA-14323: cannot add partition when DEFAULT partition exists

Solution: split the overflow partition:

ALTER TABLE RECEIVED_DOCUMENTS 
SPLIT PARTITION "OTHERS" 
VALUES ('NORWAY','ICELAND')
INTO ( PARTITION EES_COUNTRIES,
       PARTITION OTHERS
       )
UPDATE INDEXES;