feat: nullable exception handlers

reflex/app.py

@@ -422,14 +422,14 @@ class App(MiddlewareMixin, LifespanMixin):
     _background_tasks: set[asyncio.Task] = dataclasses.field(default_factory=set)
 
     # Frontend Error Handler Function
-    frontend_exception_handler: Callable[[Exception], None] = (
+    frontend_exception_handler: Callable[[Exception], None] | None = (
         default_frontend_exception_handler
     )
 
     # Backend Error Handler Function
-    backend_exception_handler: Callable[
-        [Exception], EventSpec | list[EventSpec] | None
-    ] = default_backend_exception_handler
+    backend_exception_handler: (
+        Callable[[Exception], EventSpec | list[EventSpec] | None] | None
+    ) = default_backend_exception_handler
 
     # Put the toast provider in the app wrap.
     toaster: Component | None = dataclasses.field(default_factory=toast.provider)
@@ -1620,6 +1620,10 @@ def _validate_exception_handlers(self):
             ],
             strict=True,
         ):
+            if handler_fn is None:
+                # If the handler is None, skip validation.
+                continue
+
             if hasattr(handler_fn, "__name__"):
                 _fn_name = handler_fn.__name__
             else:
@@ -1665,7 +1669,10 @@ def _validate_exception_handlers(self):
                     raise ValueError(msg)
 
             # Check if the return type is valid for backend exception handler
-            if handler_domain == "backend":
+            if (
+                handler_domain == "backend"
+                and self.backend_exception_handler is not None
+            ):
                 sig = inspect.signature(self.backend_exception_handler)
                 return_type = (
                     eval(sig.return_annotation)
@@ -1773,7 +1780,8 @@ async def process(
     except Exception as ex:
         telemetry.send_error(ex, context="backend")
 
-        app.backend_exception_handler(ex)
+        if app.backend_exception_handler is not None:
+            app.backend_exception_handler(ex)
         raise
 
 

reflex/state.py

@@ -1742,8 +1742,11 @@ async def _as_state_update(
         except Exception as ex:
             state._clean()
 
+            app = prerequisites.get_and_validate_app().app
             event_specs = (
-                prerequisites.get_and_validate_app().app.backend_exception_handler(ex)
+                app.backend_exception_handler(ex)
+                if app.backend_exception_handler is not None
+                else None
             )
 
             if event_specs is None:
@@ -1880,8 +1883,12 @@ async def _process_event(
         except Exception as ex:
             telemetry.send_error(ex, context="backend")
 
+            app = prerequisites.get_and_validate_app().app
+
             event_specs = (
-                prerequisites.get_and_validate_app().app.backend_exception_handler(ex)
+                app.backend_exception_handler(ex)
+                if app.backend_exception_handler is not None
+                else None
             )
 
             yield await state._as_state_update(
@@ -2433,9 +2440,10 @@ def handle_frontend_exception(self, info: str, component_stack: str) -> None:
             component_stack: The stack trace of the component where the exception occurred.
 
         """
-        prerequisites.get_and_validate_app().app.frontend_exception_handler(
-            Exception(info)
-        )
+        app = prerequisites.get_and_validate_app().app
+
+        if app.frontend_exception_handler is not None:
+            app.frontend_exception_handler(Exception(info))
 
 
 class UpdateVarsInternalState(State):