fix(config): correct from_yaml return type and handle empty YAML files

src/alignrl/config.py

@@ -3,10 +3,14 @@
 from __future__ import annotations
 
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import yaml
 from pydantic import BaseModel, Field
 
+if TYPE_CHECKING:
+    from typing_extensions import Self
+
 
 class BaseTrainConfig(BaseModel):
     """Shared training configuration."""
@@ -37,10 +41,10 @@ class BaseTrainConfig(BaseModel):
     load_in_4bit: bool = True
 
     @classmethod
-    def from_yaml(cls, path: Path) -> BaseTrainConfig:
+    def from_yaml(cls, path: Path) -> Self:
         with open(path) as f:
             data = yaml.safe_load(f)
-        return cls(**data)
+        return cls(**(data or {}))
 
 
 # ChatML template used as fallback when the tokenizer doesn't have one set.

tests/test_config.py

@@ -32,6 +32,18 @@ def test_from_yaml_partial(self, tmp_path: Path) -> None:
         assert cfg.model_name == "partial-model"
         assert cfg.learning_rate == 2e-4  # default preserved
 
+    def test_from_yaml_empty_file(self, tmp_path: Path) -> None:
+        yaml_path = tmp_path / "empty.yaml"
+        yaml_path.write_text("")
+        cfg = BaseTrainConfig.from_yaml(yaml_path)
+        assert cfg.model_name == "Qwen/Qwen2.5-3B"  # all defaults
+
+    def test_from_yaml_empty_doc(self, tmp_path: Path) -> None:
+        yaml_path = tmp_path / "empty_doc.yaml"
+        yaml_path.write_text("---\n")
+        cfg = BaseTrainConfig.from_yaml(yaml_path)
+        assert cfg.model_name == "Qwen/Qwen2.5-3B"
+
     def test_output_dir_is_path(self) -> None:
         cfg = BaseTrainConfig(output_dir="./my-output")
         assert isinstance(cfg.output_dir, Path)