Tools are not prompting for a password in many cases where they should

Hi Team,

When I try to using mongorestore/mongodump in CLI with password prompt and a LDAP user, the following error is thrown :

 
error parsing command line options: password required for PLAIN
 

In [the mongodb documentation|mongorestore — MongoDB Database Tools] we can read : 

To prompt the user for the password, pass the --username option without --password or specify an empty string as the --password value, as in --password="" .

I tried the following command without password argument or with --password="" but each time I got the same error :

????mongorestore -u "$USER" -password="" --authenticationDatabase '$external' --authenticationMechanism 'PLAIN' --db $DB $DB_DIR

How can I use LDAP authentication with password prompt in order to avoid writing it in the command please ?

I'm using MongoDB v4.4.5-7 on Ubuntu 18.04.5 LTS.

Thanks you beforehand.

Best Regards.

Lucas