fix falsy evaluation of build_after.count (#12136)

Author: MichelleArk

.changes/unreleased/Fixes-20251103-134034.yaml

@@ -0,0 +1,6 @@
+kind: Fixes
+body: Fix parse error when build_after.count set to 0
+time: 2025-11-03T13:40:34.653439-05:00
+custom:
+    Author: michelleark
+    Issue: "12136"

core/dbt/artifacts/resources/v1/model.py

@@ -84,14 +84,14 @@ def __post_init__(self):
         if (
             self.freshness
             and self.freshness.build_after.period
-            and not self.freshness.build_after.count
+            and self.freshness.build_after.count is None
         ):
             raise ValidationError(
                 "`freshness.build_after` must have a value for `count` if a `period` is provided"
             )
         elif (
             self.freshness
-            and self.freshness.build_after.count
+            and self.freshness.build_after.count is not None
             and not self.freshness.build_after.period
         ):
             raise ValidationError(

tests/functional/model_config/test_freshness_config.py

@@ -100,6 +100,18 @@
 """
 
 
+models__model_freshness_schema_yml_build_period_has_0_count = """
+models:
+  - name: model_a
+    description: Model with only model freshness defined
+    config:
+      freshness:
+        build_after:
+          period: day
+          count: 0
+"""
+
+
 models__model_freshness_schema_yml_build_count_requires_period = """
 models:
   - name: model_a
@@ -159,6 +171,18 @@ def test_model_freshness_configs(self, project):
         assert expected_msg in str(excinfo.value)
 
 
+class TestModelFreshnessConfigParseBuildPeriodHas0Count:
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {
+            "schema.yml": models__model_freshness_schema_yml_build_period_has_0_count,
+            "model_a.sql": models__no_freshness_sql,
+        }
+
+    def test_model_freshness_configs(self, project):
+        run_dbt(["parse"])
+
+
 class TestModelFreshnessConfigParseBuildCountRequiresPeriod:
     @pytest.fixture(scope="class")
     def models(self):