fix(router): guard update_settings against null default_litellm_params/optional_pre_call_checks

_add_router_settings_from_db_config merges config.yaml router_settings with
the DB router_settings row and calls update_settings(**combined) directly,
without going through UpdateRouterConfig's exclude_none filtering. An
explicit `default_litellm_params: null` or `optional_pre_call_checks: null`
in either source therefore reached the new elif branches verbatim:
`{**dict, **None}` and iterating `None` both raise TypeError, crashing
proxy startup / config sync.

litellm/router.py

@@ -9757,11 +9757,13 @@ class Router:
                     if value is None or isinstance(value, RetryPolicy):
                         setattr(self, var, value)
                 elif var == "default_litellm_params":
-                    self.default_litellm_params = {**self.default_litellm_params, **kwargs[var]}
+                    if kwargs[var] is not None:
+                        self.default_litellm_params = {**self.default_litellm_params, **kwargs[var]}
                 elif var == "optional_pre_call_checks":
-                    new_checks = [check for check in kwargs[var] if check not in self.optional_pre_call_checks]
-                    if new_checks:
-                        self.add_optional_pre_call_checks(new_checks)
+                    if kwargs[var] is not None:
+                        new_checks = [check for check in kwargs[var] if check not in self.optional_pre_call_checks]
+                        if new_checks:
+                            self.add_optional_pre_call_checks(new_checks)
                 else:
                     value = kwargs[var]
                     # only run routing strategy init if it has changed

tests/test_litellm/test_router.py

@@ -5401,3 +5401,21 @@ def test_get_settings_includes_default_litellm_params_and_optional_pre_call_chec
     assert settings["optional_pre_call_checks"] == ["prompt_caching"]
     assert "default_litellm_params" in settings
     assert isinstance(settings["default_litellm_params"], dict)
+
+
+def test_update_settings_tolerates_null_default_litellm_params_and_optional_pre_call_checks():
+    """
+    Regression test: `_add_router_settings_from_db_config` calls
+    `update_settings(**combined_router_settings)` with the raw dict merged from
+    config.yaml and the DB router_settings row - neither is filtered through
+    `UpdateRouterConfig(exclude_none=True)` first, so an explicit
+    `default_litellm_params: null` / `optional_pre_call_checks: null` in either
+    source reaches update_settings verbatim. `{**dict, **None}` and iterating
+    `None` both raise TypeError, which would crash proxy startup / config sync.
+    """
+    router = _make_router_for_settings_tests(timeout=42)
+
+    router.update_settings(default_litellm_params=None, optional_pre_call_checks=None)
+
+    assert router.default_litellm_params["timeout"] == 42
+    assert router.optional_pre_call_checks == []