Debug failure: Token end is child end

TypeScript Version: master

Code
Run as a fourslash test:

/// <reference path='fourslash.ts' />

// @allowJs: true
// @target: esnext

// @Filename: /a.js
//// / / ``}(a){`

verify.codeFix({
    description: "Convert to ES6 module",
    index: 0,
    newFileContent: "",
});

Expected behavior:

No assertion failures.

Actual behavior:

Error: Debug Failure. False expression: Token end is child end

fixUnusedIdentifier has been through a lot of changes and this no longer reproduces.