fix(api): reject explicit null strategy nick

app/schemas/v1.py

@@ -326,7 +326,7 @@ class StrategyCreateRequest(BaseModel):
     @classmethod
     def normalize_nick(cls, value: str | None) -> str | None:
         if value is None:
-            return None
+            raise ValueError("nick must not be null")
         normalized = value.strip()
         if not normalized:
             raise ValueError("nick must not be blank")
@@ -345,7 +345,7 @@ class StrategyUpdateRequest(BaseModel):
     @classmethod
     def normalize_nick(cls, value: str | None) -> str | None:
         if value is None:
-            return None
+            raise ValueError("nick must not be null")
         normalized = value.strip()
         if not normalized:
             raise ValueError("nick must not be blank")

tests/test_v1_strategies.py

@@ -257,7 +257,7 @@ def test_admin_create_omitting_nick_retains_legacy_generated_value() -> None:
     assert created.json()["nick"] == expected
 
 
-def test_admin_create_and_patch_accept_explicit_null_nick() -> None:
+def test_admin_create_and_patch_reject_explicit_null_nick_without_mutation() -> None:
     repo = FakeStrategyRepo()
     with _repos(repo):
         created = _client().post(
@@ -270,9 +270,11 @@ def test_admin_create_and_patch_accept_explicit_null_nick() -> None:
             json={"nick": None},
             headers=_auth("admin-token"),
         )
-    assert created.status_code == 201
-    assert changed.status_code == 200
+    assert created.status_code == 422
+    assert changed.status_code == 422
+    assert set(repo.strategies) == {"active-1", "inactive-1"}
     assert repo.strategies["active-1"].nick == "target_value:base"
+    assert repo.strategies["active-1"].revision == 1
 
 
 def test_admin_duplicate_nick_returns_conflict() -> None: