From 2286091a9a08e231e87c6e8abe7274364d7a14ad Mon Sep 17 00:00:00 2001
From: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
Date: Tue, 1 Sep 2026 18:38:38 -0700
Subject: [PATCH] fix(guardrails): skip None fields in in-memory guardrail
 updates so constructor defaults survive

---
 litellm/integrations/custom_guardrail.py       |  6 +++++-
 .../guardrail_hooks/tool_permission.py         |  8 ++++----
 .../integrations/test_custom_guardrail.py      | 18 ++++++++++++++++++
 3 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/litellm/integrations/custom_guardrail.py b/litellm/integrations/custom_guardrail.py
index 8754d116537..1562f3d092e 100644
--- a/litellm/integrations/custom_guardrail.py
+++ b/litellm/integrations/custom_guardrail.py
@@ -1298,6 +1298,9 @@ class CustomGuardrail(CustomLogger):
         resync ``event_hook`` when the update carries a new ``mode``. The new
         mode is validated against ``supported_event_hooks`` before any state
         is mutated, so a rejected update leaves the guardrail untouched.
+        ``None`` values are skipped because both sources serialize every unset
+        LitellmParams field as ``None``; applying them would clobber
+        constructor-derived state (e.g. dict defaults) with ``None``.
         """
         updated_params: Final[Mapping[str, object]] = (
             litellm_params if isinstance(litellm_params, Mapping) else vars(litellm_params)
@@ -1307,7 +1310,8 @@ class CustomGuardrail(CustomLogger):
         if new_event_hook is not None and self.supported_event_hooks:
             self._validate_or_warn_event_hook(new_event_hook, self.supported_event_hooks)
         for key, value in updated_params.items():
-            setattr(self, key, value)
+            if value is not None:
+                setattr(self, key, value)
         if new_event_hook is not None:
             self.event_hook = new_event_hook
 
diff --git a/litellm/proxy/guardrails/guardrail_hooks/tool_permission.py b/litellm/proxy/guardrails/guardrail_hooks/tool_permission.py
index 88e24db207a..d6bea312031 100644
--- a/litellm/proxy/guardrails/guardrail_hooks/tool_permission.py
+++ b/litellm/proxy/guardrails/guardrail_hooks/tool_permission.py
@@ -176,10 +176,10 @@ class ToolPermissionGuardrail(CustomGuardrail):
         super().update_in_memory_litellm_params(litellm_params)
 
         # The generic update above sets ``self.rules`` from the incoming value
-        # (None on a partial update that omits rules), but never rebuilds the
-        # compiled maps. Rebuild them when rules are provided; otherwise restore
-        # the previous ruleset so a partial update doesn't silently wipe it. An
-        # explicit empty list still clears the rules.
+        # (skipping None) but never rebuilds the compiled maps. Rebuild them
+        # when a rules list is provided; otherwise restore the previous ruleset
+        # so a non-list value can't silently wipe it. An explicit empty list
+        # still clears the rules.
         rules: Final = params.get("rules")
         if isinstance(rules, list):
             try:
diff --git a/tests/test_litellm/integrations/test_custom_guardrail.py b/tests/test_litellm/integrations/test_custom_guardrail.py
index c84fcd5ac11..3983f698ef0 100644
--- a/tests/test_litellm/integrations/test_custom_guardrail.py
+++ b/tests/test_litellm/integrations/test_custom_guardrail.py
@@ -2281,6 +2281,24 @@ class TestUpdateInMemoryLitellmParams:
         assert getattr(guardrail, "api_base", None) == "https://guardrail.example.com"
         assert guardrail.should_run_guardrail(data={}, event_type=GuardrailEventHooks.post_call) is True
 
+    def test_none_values_do_not_clobber_constructor_state(self):
+        guardrail = self._guardrail()
+        guardrail.additional_provider_specific_params = {"team": "security"}
+        guardrail.api_base = "https://guardrail.example.com"
+
+        guardrail.update_in_memory_litellm_params(
+            {
+                "mode": "post_call",
+                "api_base": None,
+                "additional_provider_specific_params": None,
+                "extra_headers": None,
+            }
+        )
+
+        assert guardrail.additional_provider_specific_params == {"team": "security"}
+        assert guardrail.api_base == "https://guardrail.example.com"
+        assert guardrail.event_hook is GuardrailEventHooks.post_call
+
     def test_strict_mode_rejects_unsupported_mode_without_mutating(self, monkeypatch):
         monkeypatch.delenv("LITELLM_STRICT_GUARDRAIL_MODES", raising=False)
         guardrail = self._guardrail()