Safari 11.1: ajax/XHR form submission fails when input[type=file] is empty

Question

UPDATE: As of Webkit build r230963, this issue has been resolved in Webkit.

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Since the recent Safari 11.1 update on macOS and iOS, as

Answer 1

As of Webkit build r230963, this issue has been resolved in Webkit. I downloaded and ran that build and confirmed the issue is resolved. Not idea when a public release will be available for Safari that contains this fix.