Thank you for reporting this issue. Going through the batch update code, we could not see why a user with an empty email address would not be found by username. Leaving the email box blank should still match an empty email. We need a little more detail to look into this.
Which exact 2.2 version are you running?
What exactly happens when you search by username: a 'No items matched your filter' error, or a batch that completes but leaves the user in place?
Which criteria did you fill in on the Batch update users page (username only, or exact match, user group, state, or others too), and was the email box left blank?
How did this user end up with no email address: registered through a connected account, imported, created by an add-on, or edited directly in the database?
Is the user an administrator or moderator?
This is an automated assessment. A member of staff may review and update it.