It is possible to submit a close vote in the moderator migration interface without selecting a migration target.
To reproduce on the moderator close dialog:
Select "off-topic because..." and "This question belongs on another site in the Stack Exchange network"
Enter some dummy text under "belongs on another site in the Stack Exchange network" but do not select any autocomplete suggestion. The "Vote to Close" button will still be grayed out.
Select any default option in the list of migration targets. The "Vote to Close" button will activate.
Re-select "belongs on another site in the Stack Exchange network" which still has your dummy text.
Click the now-active "Vote to Close" button.
Bug: You will observe a brief error message (along the lines of "There was an error" or "Action could not be completed"). The question will not be migrated anywhere, but you will add one non-binding close vote to the vote total, despite normally casting a binding close vote as a mod. You can submit multiple close votes in this way; submitting one close vote in this way does not stop you from immediately submitting more.
The related bug that led to discover this bizarre set of steps was that in Chrome on Android, there were no autocomplete suggestions (but that's a separate bug, I guess).