Do not initialize members to null in "process a URLPatternInit"

[jeremyroman]

It is not valid for these dictionary members to be null, since they are defined to, if present, hold a USVString value. Instead, these should be omitted from the result dictionary altogether if no string was provided to this algorithm.

This addresses the concern raised in #202 (comment).

• At least two implementers are interested (and none opposed):
  • Google Chrome
  • n/a (change is simply fixing a bug in a non-controversial way, per this comment)
• Tests are written and can be reviewed and commented upon at:
  • n/a (this is a fix to how the spec expresses this, but does not represent a behavior change, and existing tests cover this behavior)
• Implementation bugs are filed:
  • Chromium: n/a (believed to work correctly in Chromium)
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=1731418 (vendor does not yet implement the spec)
  • WebKit: [no known URLPattern bug] (vendor does not yet implement the spec)
  • Deno: n/a (no reason to believe a change is required)
  • kenchris/urlpattern-polyfill: n/a (no reason to believe a change is required)
• MDN issue is filed: n/a (change is on a spec detail not expressly documented)
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

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[sisidovski]

Thanks! It looks the PR preview failed to build. Could you try the build again?

[jeremyroman]

Not sure how to get pr-preview to reattempt, but a preview is available here: https://api.csswg.org/bikeshed/?url=https%3A%2F%2Fraw.githubusercontent.com%2Fjeremyroman%2Furlpattern%2Fprocess-urlpatterninit-null%2Fspec.bs&force=1&md-status=LS-PR&md-Text-Macro=PR-NUMBER%20212

[sisidovski]

After this change, the result of process a URLPatternInit may not have corresponding keys. We don't set null to map entires.

Basically LGTM but let me ask a beginner question. Accessing to the absent key to the map is considered as null? In initialize, there're some steps calling complie a compoennt with map entries. In the step 1 in "compile a component", the input is expected to be null.

[sisidovski]

#214 clarified my previous comment. LGTM

[jeremyroman]

It is an assertion failure to get an entry from a map that it does not contain. https://infra.spec.whatwg.org/#map-get