sudo hdparm --user-master u --security-set-pass NULL /dev/sda

security_password: ""

/dev/sda:
Issuing SECURITY_SET_PASS command, password="", user=user, mode=high

Security:
       Master password revision code = 65534
               supported
               enabled
       not     locked
       not     frozen
       not     expired: security count
               supported: enhanced erase
       Security level high
       2min for SECURITY ERASE UNIT. 2min for ENHANCED SECURITY ERASE UNIT.

sudo hdparm --user-master u --security-set-pass 0000 /dev/sda

security_password: "0000"

/dev/sda:
Issuing SECURITY_SET_PASS command, password="", user=user, mode=high

hdparm --user-master u --security-erase 0000 /dev/sda

security_password: "0000"
/dev/sda: Permission denied

hdparm --user-master u --security-erase NULL /dev/sda

security_password: ""
/dev/sda: Permission denied

sudo hdparm --security-disable 0000
sudo hdparm --security-disable NULL
sudo hdparm --security-disable PWD
sudo hdparm --security-disable ""
sudo hdparm --security-disable

missing PASSWD

Security:
       Master password revision code = 65534
               supported
               enabled
       not     locked
       not     frozen
       not     expired: security count
               supported: enhanced erase
       Security level high
       2min for SECURITY ERASE UNIT. 2min for ENHANCED SECURITY ERASE UNIT.