ORA-39002 followed by ORA-39168 on impdp with sqlfile parameter

Hi Gurus,

I am with the following environment.  Oracle Linux 7(64 bit) with Oracle EE Database 12.2.0.1.0.

I am doing expdp at schema level.  I issued the following command.

expdp 'username/password' directory=directory_name dumpfile=dump_filename logfile=logfile.log schemas=schema_name

The above command exported the schema_name I wanted successfully.

Now I want to gather constraints sql statements only in an sqlfile.

I used the following command:

impdp 'username/password' directory_name=dir_name dumpfile=dump_filename logfile=logfile.log include=constraint sqlfile=const.sql

It produces the following error:

ORA-39002: invalid operation

ORA-39168: Object path CONSTRAINT was not found.