[BUGFIX] prevent errors when updating user (#5742)

# Description
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Please also include relevant motivation and context. List any
dependencies that are required for this change. -->

This PR resolves some errors found after changes included in #5615.

**Type of change**
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PR according to the type of change -->

- Bug fix (non-breaking change which fixes an issue)


**How Has This Been Tested**
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**Checklist**
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- I added relevant documentation
- I followed the style guidelines of this project
- I did a self-review of my code
- I made corresponding changes to the documentation
- I confirm My changes generate no new warnings
- I have added tests that prove my fix is effective or that my feature
works
- I have added relevant notes to the CHANGELOG.md file (See
https://keepachangelog.com/)

argilla/src/argilla/_api/_users.py

@@ -45,7 +45,7 @@ def create(self, user: UserModel) -> UserModel:
 
     @api_error_handler
     def update(self, user: UserModel) -> UserModel:
-        json_body = user.model_dump()
+        json_body = user.model_dump(exclude_unset=True)
         response = self.http_client.patch(f"/api/v1/users/{user.id}", json=json_body).raise_for_status()
         user_updated = self._model_from_json(response_json=response.json())
         self._log_message(message=f"Updated user {user_updated.username}")

argilla/src/argilla/_models/_user.py

@@ -16,6 +16,7 @@
 from typing import Optional
 
 from pydantic import field_validator, ConfigDict
+from pydantic_core.core_schema import ValidationInfo
 
 from argilla._models import ResourceModel
 
@@ -43,12 +44,12 @@ class UserModel(ResourceModel):
 
     @field_validator("first_name")
     @classmethod
-    def __validate_first_name(cls, v, values):
+    def __validate_first_name(cls, v, info: ValidationInfo):
         """Set first_name to username if not provided"""
         if isinstance(v, str):
             return v
         elif not v:
-            return values["username"]
+            return info.data["username"]
 
     @field_validator("username", mode="before")
     @classmethod

argilla/tests/integration/test_manage_users.py

@@ -64,6 +64,18 @@ def test_update_user(self, client: Argilla):
         assert updated_user.last_name == "Updated Last Name"
         assert updated_user.role == "admin"
 
+    def test_update_user_role(self, client: Argilla):
+        user = User(username=f"test_update_user_{uuid.uuid4()}", password="test_password")
+        client.users.add(user)
+
+        user = client.users(username=user.username)
+
+        user.role = "admin"
+        user.update()
+
+        updated_user = client.users(id=user.id)
+        assert updated_user.role == "admin"
+
     def test_update_user_with_duplicate_username(self, client: Argilla):
         user1 = User(username=f"test_user1_{uuid.uuid4()}", password="test_password")
         user2 = User(username=f"test_user2_{uuid.uuid4()}", password="test_password")

argilla/tests/unit/test_resources/test_users.py

@@ -322,3 +322,9 @@ def test_create_user(self, httpx_mock: HTTPXMock):
             assert user.id == user_id
             assert user.username == "test-user"
             assert user.password == "test-password"
+
+
+class TestUserModel:
+    def test_create_user_with_empty_first_name(self):
+        user = UserModel(username="test-user", first_name=None)
+        assert user.first_name is user.username