Fixed null.split(':') crashes

Summary:
_extractHostFromHttpHost('') or _extractHostFromHttpHost(null) returns null (line 281-283), then _computeETLDPlus1ForHost calls _isIPAddress(null) → _isIPv6Address(null) → null.split(':') crashes.

The minimal fix is to bail out of _computeETLDPlus1ForHost when hostname is falsy. Downstream CookieSettings already accepts a null domain (cookie just won't have one), and processRequest resets etld_plus_1 = null at the top, so leaving it null is consistent.

My current fix (option A) — early-return in _computeETLDPlus1ForHost:

✅ Targeted, clear intent at the call site where the null actually originates
✅ Avoids a latent precedence bug at line 255 (more on this below)
❌ Doesn't protect other future callers of _isIPv6Address / _isIPAddress

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overriding_review_checks_triggers_an_audit_and_retroactive_review
Oncall Short Name: advertiser_experience_foundations

Differential Revision: D104759549

fbshipit-source-id: 349b7edba71c1e082359e0530feec30fd73db1a9

Author: Jiaming You

nodejs/capi-param-builder/src/ParamBuilder.js

@@ -246,6 +246,11 @@ class ParamBuilder {
       // in case a new host is passed in for the same request
       this.host = host;
       const hostname = this._extractHostFromHttpHost(host);
+      if (!hostname) {
+        this.etld_plus_1 = null;
+        this.sub_domain_index = 0;
+        return;
+      }
       if (this._isIPAddress(hostname)) {
         this.etld_plus_1 = this._maybeBracketIPv6(hostname);
         this.sub_domain_index = 0;