diff --git a/tests/tools/test_memory_tool.py b/tests/tools/test_memory_tool.py
index a7c822cb18d..c2903f375c6 100644
--- a/tests/tools/test_memory_tool.py
+++ b/tests/tools/test_memory_tool.py
@@ -535,6 +535,26 @@ class TestMemoryToolDispatcher:
         result = json.loads(memory_tool(action="add", target="invalid", content="x", store=store))
         assert result["success"] is False
 
+    def test_null_target_defaults_to_memory_store(self, store):
+        result = json.loads(
+            memory_tool(
+                action="add",
+                target=None,
+                content="Project uses pytest with xdist.",
+                store=store,
+            )
+        )
+        assert result["success"] is True
+        assert store.memory_entries == ["Project uses pytest with xdist."]
+        assert store.user_entries == []
+
+    def test_invalid_non_string_target_still_rejected(self, store):
+        result = json.loads(
+            memory_tool(action="add", target=42, content="via tool", store=store)
+        )
+        assert result["success"] is False
+        assert "Invalid target" in result["error"]
+
     def test_unknown_action(self, store):
         result = json.loads(memory_tool(action="unknown", store=store))
         assert result["success"] is False
diff --git a/tools/memory_tool.py b/tools/memory_tool.py
index 02315bd0726..08eeaa470ea 100644
--- a/tools/memory_tool.py
+++ b/tools/memory_tool.py
@@ -977,6 +977,12 @@ def memory_tool(
     if store is None:
         return tool_error("Memory is not available. It may be disabled in config or this environment.", success=False)
 
+    # Some strict providers fill optional schema fields with JSON null rather
+    # than omitting them.  Treat ``target: null`` as omitted so memory writes
+    # still use the documented default store instead of failing validation.
+    if target is None:
+        target = "memory"
+
     if target not in {"memory", "user"}:
         return tool_error(f"Invalid target '{target}'. Use 'memory' or 'user'.", success=False)