Add test case for bug #103.
Normalize empty URI parts to `null`. Fixes #103.
#103: Add test case for an equivalent case that is still broken.
#103: Set parts.protocol to null, not empty string.
#103: Fix tests that expect protocol: "" for scheme-relative URIs.
#103: Fix case where missing scheme sets parts.protocol = "".
Merge fixing inconsistent `.relativeTo()` results caused by inconsistent URI component values
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