If one sets 'Defaults rootpw' in sudoers but no root password is it disaster?

[Chris Green <cl@isbd.net>]

I'd like to force a different password from my own password when I do
'sudo -i' to get root privilege.  However I'm a bit frightened about
what might happen if I set 'Defaults rootpw' in the sudoers file but
forget to actually create a root password. (This is on systems where, 
previously, I've never had a root password).

Would this totally lock me out from becoming root? Would the only way
out be to boot into single user mode to mend things?

... or is visudo clever enough to spot this?

-- 
Chris Green
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