Fixes #9742 (#9767)

* Fixes #9742

Validator was not handling situation where function does not return anything.

Signed-off-by: Richard Decal <public@richarddecal.com>

* add test case for function which doesn't return anything

Signed-off-by: Richard Decal <public@richarddecal.com>

* format

* add changeset

---------

Signed-off-by: Richard Decal <public@richarddecal.com>
Co-authored-by: Abubakar Abid <abubakar@huggingface.co>
Co-authored-by: gradio-pr-bot <gradio-pr-bot@users.noreply.github.com>

.changeset/happy-lies-study.md

@@ -0,0 +1,5 @@
+---
+"gradio": patch
+---
+
+fix:Fixes #9742

gradio/blocks.py

@@ -1744,6 +1744,10 @@ Received inputs:
         [{received}]"""
                 )
             else:
+                if len(predictions) == 1 and predictions[0] is None:
+                    # do not throw error if the function did not return anything
+                    # https://github.com/gradio-app/gradio/issues/9742
+                    return
                 warnings.warn(
                     f"""A function{name} returned too many output values (needed: {len(dep_outputs)}, returned: {len(predictions)}). Ignoring extra values.
     Output components:

test/test_blocks.py

@@ -8,6 +8,7 @@ import random
 import sys
 import time
 import uuid
+import warnings
 from concurrent.futures import wait
 from contextlib import contextmanager
 from functools import partial
@@ -703,6 +704,26 @@ class TestBlocksPostprocessing:
                 demo.fns[0], predictions=["test", "test2", "test3"], state=None
             )
 
+    @pytest.mark.asyncio
+    async def test_no_warning_if_func_has_no_outputs(self):
+        """
+        Ensures that if a function has no outputs, no warning is raised.
+        """
+        with gr.Blocks() as demo:
+            button = gr.Button()
+
+            def no_return():
+                pass
+
+            button.click(
+                no_return,
+                inputs=None,
+                outputs=None,
+            )
+        with warnings.catch_warnings():
+            warnings.simplefilter("error")
+            await demo.postprocess_data(demo.fns[0], predictions=None, state=None)  # type: ignore
+
     @pytest.mark.asyncio
     async def test_error_raised_if_num_outputs_mismatch_with_function_name(self):
         def infer(x):