[Bug]: an error at saving a multiple block when un-checking guids

[ioanarusiczki]

What happened?

Followup https://github.com/mozilla/addons/issues/15013

1. Go to admin and make a multiple block (add the guids line by line)
2. on the next page -> un-check one of the guids and try to submit the block

What did you expect to happen?

This cannot be saved because of the above error.

So I've created soft blocks separately https://addons-internal.dev.mozaws.net/en-US/admin/models/blocklist/blocklistsubmission/759/change/

And hard blocks into a different one https://addons-internal.dev.mozaws.net/en-US/admin/models/blocklist/blocklistsubmission/758/change/

Is there an existing issue for this?

• [X] I have searched the existing issues

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