Your Mac asks you to enter the name and password of an administrator account when it needs to verify that you have permission to make changes. For example, you must authenticate as an administrator when you click the lock 
in System Preferences, enter certain commands in Terminal, or set a firmware password.
The password of the administrator account should not be blank. Your Mac might not accept a blank password, even if the account is using a blank password.
Learn how to change or reset the password of a macOS user account.