Describe the bug

I created an image component with source = upload, type = numpy, tool = sketch.
Then, attempted to override its upload method with a simple edit diversion.
However, this broke the regular upload functionality, with any simple png image (which obviously worked before) - apparently it's trying to read the mask content in components.preprocess, but doesn't have a fallback in case mask is None, as is the case for the input images I used.

A simple exception clause when setting mask_im should suffice, I think.
Another assertion breaks in preprocess if I set this image via another component's update: assert isinstance(x, dict) . For that one there at least seems to be a workaround of setting the component to a dict in the first place (with a null mask).
Actually looks like I can't, because postprocess expects only images, no dict. 🤦‍♂️
Note that the preprocess assertion error occurs after 2-3 overwrites, receives a base64 str.

Is there an existing issue for this?

• I have searched the existing issues

Reproduction

import gradio as gr
def detect_image_colours(img):
    return img

with gr.Blocks() as demo:
    with gr.Row():
        with gr.Column():
            sketch = gr.Image(source = "upload", mirror_webcam = False, type = "numpy", tool = "sketch")
    sketch.upload(fn = detect_image_colours, inputs = [sketch], outputs = [sketch])

if __name__ == "__main__":
    demo.launch()

1. Attempt to upload png image to sketch component.

Screenshot

No response

Logs

Running on local URL:  http://127.0.0.1:7860

To create a public link, set `share=True` in `launch()`.
Traceback (most recent call last):
  File "C:\Python38\lib\site-packages\gradio\routes.py", line 338, in run_predict
    output = await app.get_blocks().process_api(
  File "C:\Python38\lib\site-packages\gradio\blocks.py", line 1013, in process_api
    inputs = self.preprocess_data(fn_index, inputs, state)
  File "C:\Python38\lib\site-packages\gradio\blocks.py", line 911, in preprocess_data
    processed_input.append(block.preprocess(inputs[i]))
  File "C:\Python38\lib\site-packages\gradio\components.py", line 1508, in preprocess
    mask_im = processing_utils.decode_base64_to_image(mask)
  File "C:\Python38\lib\site-packages\gradio\processing_utils.py", line 53, in decode_base64_to_image
    content = encoding.split(";")[1]
AttributeError: 'NoneType' object has no attribute 'split'

System Info

Gradio = 3.16.2
OS = Windows 10
Browser = Chrome

Severity

annoying