chore: treat empty-string env vars as absent in Configuration

[vdusek]

Description

The Apify platform sometimes sets some env vars to an empty string instead of leaving them unset (see #303, or this Discord thread). For fields whose type can't parse '', validation raised and crashed Actor.init().

A few fields were already guarded against this with ad-hoc BeforeValidator lambdas. This PR consolidates them into a single shared _default_if_empty helper and defensively applies the same fallback to the remaining typed / JSON fields, so any field that starts arriving as '' falls back to its default instead of crashing.

Why chore and not fix

I verified against the current apify-worker code (getEnvsForActor in act2_run_job.ts). Only four env vars are actually emitted as '' today, and those were already handled:

• max_paid_dataset_items (maxItems ? String(...) : '')
• max_total_charge_usd (maxTotalChargeUsd ? String(...) : '')
• timeout_at (timeoutAt ? toISOString() : '')
• user_is_paying (isRunOfPayingUser ? '1' : '')

The remaining fields are covered defensively. The worker always gives them a real value (started_at, dedicated_cpus, proxy_port, web_server_port, is_at_home), never sets them at all (metamorph_after_sleep, test_pay_per_event), or returns at least {} for the JSON ones (charged_event_counts, and pricing). The worker also wraps every value in String(...), so an unset value reaches the Actor as the literal "undefined", not ''.

So this doesn't fix an observed crash. It's cleanup (consolidating the lambdas) plus hardening for the future, hence chore.

Changes

• Added a shared _default_if_empty(default=...) validator and replaced the existing ad-hoc lambdas (timeout_at, max_paid_dataset_items, max_total_charge_usd, user_is_paying) with it.
• Applied it defensively to started_at, dedicated_cpus, proxy_port, web_server_port, metamorph_after_sleep, is_at_home, test_pay_per_event.
• JSON fields (ACTOR_STORAGES_JSON, APIFY_CHARGED_ACTOR_EVENT_COUNTS): treat '' as absent instead of letting json.loads('') raise, mirroring the existing _parse_actor_pricing_info behavior.
• Regression tests for all affected env vars.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.91%. Comparing base (0daca28) to head (5cc2a2a).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #965      +/-   ##
==========================================
+ Coverage   89.90%   89.91%   +0.01%     
==========================================
  Files          49       49              
  Lines        3091     3095       +4     
==========================================
+ Hits         2779     2783       +4     
  Misses        312      312              

Flag	Coverage Δ
e2e	35.96% <66.66%> (+0.05%)	⬆️
integration	56.93% <100.00%> (+0.05%)	⬆️
unit	78.77% <100.00%> (+0.02%)	⬆️

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[Pijukatel]

Isn't this actually less defensive?

Is there any actual use case for having 'ACTOR_STORAGES_JSON' be set as an empty string? The env variable clearly states it should be a json. So either have json there, or don't set the variable.

Code should not try to guess the intention from an ambiguous action. And here we are guessing that an empty env variable probably means the user did not want to set it up in the first place...