Passing `gist` URL parameter twice breaks playground

Normally, if you pass something invalid for the gist, the playground just opens with an empty textarea. But if you pass it twice, the page doesn't load at all. (Q: How could that happen / why would you do that? A: by mistake, but it happened)

This link shows a completely blank page for me in Firefox and Chrome (macOS): https://play.rust-lang.org/?gist=break&gist=rust

The error console shows:

TypeError: "Parameter 'url' must be a string, not object"
    parse https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:1
    b https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:1
    resolve https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:1
    resolve https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:1
    Bt https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:13
    r https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:6
    dispatch https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:1
    Ut https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:13
    r https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:6
    l https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:13
    router https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:13
    Rr https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:13
    gi https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    La https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    yu https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    sl https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    ul https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    Ju https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    Ku https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    Fl https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    l https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    tl https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    $l https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    render https://play.rust-lang.org/assets/13f807a13f5fc9461372.js:22
    511 https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:13
    c https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:1
    239 https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:1
    c https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:1
    a https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:1
    <anonymous> https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:1
    <anonymous> https://play.rust-lang.org/assets/c6dbac6de476402e0d00.js:1
13f807a13f5fc9461372.js:22:82385

Reproduce the failure with https://play.rust-lang.org/?gist=break&gist=rust in Firefox or Chrome and inspect the query-parameter handling behind the reported TypeError. Trace how the repeated gist value reaches the playground router, then verify that the page loads with an empty textarea instead of becoming blank.