fix: Fix BeforeValidator treating 0 as falsy in configuration fields (#819)

## Summary

- The `BeforeValidator(lambda val: val or None)` on
`max_paid_dataset_items` and `max_total_charge_usd` configuration fields
treated `0` as falsy, converting it to `None`. This meant a legitimate
value of `0` (e.g. a zero charge limit) would be silently discarded.
- Replaced with `lambda val: val if val != '' else None` which only
converts empty strings (from unset env vars) to `None`, preserving `0`
as a valid value.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: vdusek

src/apify/_configuration.py

@@ -295,7 +295,7 @@ class Configuration(CrawleeConfiguration):
             alias='actor_max_paid_dataset_items',
             description='For paid-per-result Actors, the user-set limit on returned results. Do not exceed this limit',
         ),
-        BeforeValidator(lambda val: val or None),
+        BeforeValidator(lambda val: val if val != '' else None),
     ] = None
 
     max_total_charge_usd: Annotated[
@@ -304,7 +304,7 @@ class Configuration(CrawleeConfiguration):
             alias='actor_max_total_charge_usd',
             description='For pay-per-event Actors, the user-set limit on total charges. Do not exceed this limit',
         ),
-        BeforeValidator(lambda val: val or None),
+        BeforeValidator(lambda val: val if val != '' else None),
     ] = None
 
     test_pay_per_event: Annotated[

tests/unit/actor/test_configuration.py

@@ -1,4 +1,5 @@
 import json
+from decimal import Decimal
 from pathlib import Path
 
 import pytest
@@ -275,6 +276,34 @@ def test_default_values() -> None:
     assert config.test_pay_per_event is False
 
 
+def test_max_paid_dataset_items_zero_is_preserved(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Test that max_paid_dataset_items=0 is not treated as falsy and converted to None."""
+    monkeypatch.setenv('ACTOR_MAX_PAID_DATASET_ITEMS', '0')
+    config = ApifyConfiguration()
+    assert config.max_paid_dataset_items == 0
+
+
+def test_max_total_charge_usd_zero_is_preserved(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Test that max_total_charge_usd=0 is not treated as falsy and converted to None."""
+    monkeypatch.setenv('ACTOR_MAX_TOTAL_CHARGE_USD', '0')
+    config = ApifyConfiguration()
+    assert config.max_total_charge_usd == Decimal(0)
+
+
+def test_max_paid_dataset_items_empty_string_becomes_none(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Test that an empty env var for max_paid_dataset_items is converted to None."""
+    monkeypatch.setenv('ACTOR_MAX_PAID_DATASET_ITEMS', '')
+    config = ApifyConfiguration()
+    assert config.max_paid_dataset_items is None
+
+
+def test_max_total_charge_usd_empty_string_becomes_none(monkeypatch: pytest.MonkeyPatch) -> None:
+    """Test that an empty env var for max_total_charge_usd is converted to None."""
+    monkeypatch.setenv('ACTOR_MAX_TOTAL_CHARGE_USD', '')
+    config = ApifyConfiguration()
+    assert config.max_total_charge_usd is None
+
+
 def test_max_total_charge_usd_decimal_parsing(monkeypatch: pytest.MonkeyPatch) -> None:
     """Test that max_total_charge_usd is parsed as Decimal from env var."""
     from decimal import Decimal