MAINT: Handle empty manifest files

Author: nourinmohd

src/fmu/dataio/manifest/_models.py

@@ -37,7 +37,12 @@ def __len__(self) -> int:
     def from_file(cls, manifest_path: Path) -> Self:
         """Load the export manifest from the JSON file."""
         with manifest_path.open("r", encoding="utf-8") as file:
-            return cls.model_validate(json.load(file))
+            content = file.read()
+
+        if not content.strip():
+            return cls()
+
+        return cls.model_validate(json.loads(content))
 
     def add_entry(self, absolute_path: Path) -> None:
         """Append a new file to the manifest."""

tests/test_units/test_manifest.py

@@ -49,6 +49,16 @@ def test_export_manifest_from_file_not_exist(tmp_path: Path) -> None:
         ExportManifest.from_file(tmp_path / MANIFEST_FILENAME)
 
 
+def test_export_manifest_from_empty_file(tmp_path: Path) -> None:
+    """Test that an empty manifest file is loaded as a new manifest."""
+    manifest_path = tmp_path / MANIFEST_FILENAME
+    manifest_path.touch()
+
+    manifest = ExportManifest.from_file(manifest_path)
+
+    assert len(manifest) == 0
+
+
 def test_get_manifest_path_realization_context(runpath_no_dotfmu: Path) -> None:
     """Test that the manifest path is correctly derived in a realization context."""
     # check test assumption that the fixture points to the runpath