diff --git a/substra/sdk/schemas.py b/substra/sdk/schemas.py
index bb9a0a3d..06683e7b 100644
--- a/substra/sdk/schemas.py
+++ b/substra/sdk/schemas.py
@@ -146,6 +146,24 @@ class DataSampleSpec(_Spec):
     def is_many(self):
         return self.paths and len(self.paths) > 0
 
+    @pydantic.field_validator("paths")
+    @classmethod
+    def resolve_paths(cls, v: List[pathlib.Path]) -> List[pathlib.Path]:
+        """Resolve given paths."""
+        if v is None:
+            raise ValueError("'paths' cannot be set to None.")
+
+        return [p.resolve() for p in v]
+
+    @pydantic.field_validator("path")
+    @classmethod
+    def resolve_path(cls, v: pathlib.Path) -> pathlib.Path:
+        """Resolve given path."""
+        if v is None:
+            raise ValueError("'path' cannot be set to None.")
+
+        return v.resolve()
+
     @pydantic.model_validator(mode="before")
     @classmethod
     def exclusive_paths(cls, values: typing.Any) -> typing.Any:
@@ -156,24 +174,6 @@ def exclusive_paths(cls, values: typing.Any) -> typing.Any:
             raise ValueError("'path' or 'paths' field must be set.")
         return values
 
-    @pydantic.model_validator(mode="before")
-    @classmethod
-    def resolve_paths(cls, values: typing.Any) -> typing.Any:
-        """Resolve given path is relative."""
-        if "paths" in values:
-            paths = []
-            for path in values["paths"]:
-                path = pathlib.Path(path)
-                paths.append(path.resolve())
-
-            values["paths"] = paths
-
-        elif "path" in values:
-            path = pathlib.Path(values["path"])
-            values["path"] = path.resolve()
-
-        return values
-
     @contextlib.contextmanager
     def build_request_kwargs(self, local):
         # redefine kwargs builder to handle the local paths
diff --git a/tests/sdk/test_schemas.py b/tests/sdk/test_schemas.py
index 359a33d5..9c50c757 100644
--- a/tests/sdk/test_schemas.py
+++ b/tests/sdk/test_schemas.py
@@ -28,3 +28,13 @@ def test_datasample_spec_exclusive_path():
 def test_datasample_spec_no_path():
     with pytest.raises(ValueError):
         DataSampleSpec(data_manager_keys=[str(uuid.uuid4())])
+
+
+def test_datasample_spec_paths_set_to_none():
+    with pytest.raises(ValueError):
+        DataSampleSpec(paths=None, data_manager_keys=[str(uuid.uuid4())])
+
+
+def test_datasample_spec_path_set_to_none():
+    with pytest.raises(ValueError):
+        DataSampleSpec(path=None, data_manager_keys=[str(uuid.uuid4())])