You can also set up the assignment initially so the 'Display Grade as' option is set to 'Incomplete/Complete'. then, after saving and publishing the assignment, visit the Grade Book and set the column default grade to 'Incomplete'. Then return to the assignment and alter the 'Display Grade as' option to 'Percentage', saving the new assignment settings. When you go back to the Grade Book it will have turned all those 'Incomplete's into '0%'s.
It's a minor faff I know, but it's doable, and was used in a two-part video-creation-and-then-peer-review type assignment here (University of Stirling, Scotland) last year where the tutor wanted to show to students that they would get 0% unless they engaged with the peer review part as well.
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