Fix a bug when loading empty yaml file (#330)

Co-authored-by: Sydney Runkle <54324534+sydney-runkle@users.noreply.github.com>

pydantic_settings/sources.py

@@ -1692,7 +1692,7 @@ def __init__(
     def _read_file(self, file_path: Path) -> dict[str, Any]:
         import_yaml()
         with open(file_path, encoding=self.yaml_file_encoding) as yaml_file:
-            return yaml.safe_load(yaml_file)
+            return yaml.safe_load(yaml_file) or {}
 
 
 def _get_env_var_key(key: str, case_sensitive: bool = False) -> str:

tests/test_settings.py

@@ -3485,6 +3485,29 @@ def settings_customise_sources(
     assert s.model_dump() == {}
 
 
+@pytest.mark.skipif(yaml is None, reason='pyYaml is not installed')
+def test_yaml_empty_file(tmp_path):
+    p = tmp_path / '.env'
+    p.write_text('')
+
+    class Settings(BaseSettings):
+        model_config = SettingsConfigDict(yaml_file=p)
+
+        @classmethod
+        def settings_customise_sources(
+            cls,
+            settings_cls: Type[BaseSettings],
+            init_settings: PydanticBaseSettingsSource,
+            env_settings: PydanticBaseSettingsSource,
+            dotenv_settings: PydanticBaseSettingsSource,
+            file_secret_settings: PydanticBaseSettingsSource,
+        ) -> Tuple[PydanticBaseSettingsSource, ...]:
+            return (YamlConfigSettingsSource(settings_cls),)
+
+    s = Settings()
+    assert s.model_dump() == {}
+
+
 @pytest.mark.skipif(sys.version_info <= (3, 11) and tomli is None, reason='tomli/tomllib is not installed')
 def test_toml_file(tmp_path):
     p = tmp_path / '.env'