R1:be21dd3b52b8

Fix some "URI->alter(X, null)" callsites

Summary:
Ref T13250. This internally calls `replaceQueryParam(X, null)` now, which fatals if the second parameter is `null`. I hit these legitimately, but I'll look for more callsites and follow up by either allowing this, removing `alter()`, fixing the callsites, or some combination.

(I'm not much of a fan of `alter()`.)

Test Plan: Browsing a paginated list no longer complains about URI construction.

Reviewers: amckinley

Reviewed By: amckinley

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