diff --git a/api/core/tools/custom_tool/tool.py b/api/core/tools/custom_tool/tool.py
index 2f5cc6d4c0..5cba4cf7f5 100644
--- a/api/core/tools/custom_tool/tool.py
+++ b/api/core/tools/custom_tool/tool.py
@@ -213,7 +213,8 @@ class ApiTool(Tool):
                         elif "default" in property:
                             body[name] = property["default"]
                         else:
-                            body[name] = None
+                            # omit optional parameters that weren't provided, instead of setting them to None
+                            pass
                     break
 
         # replace path parameters