fix: handle None return from error handler in no-output background callbacks - #4012
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dajiaohuang wants to merge 2 commits into
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dajiaohuang wants to merge 2 commits into
dajiaohuang wants to merge 2 commits into
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…llbacks When a background callback with no outputs raises an exception, the error handler is called. If the error handler returns None, the code was incorrectly setting output_value = NoUpdate(), which then triggered an InvalidCallbackReturnValue exception at the output validation step. This change adds the same output_spec check that exists in the non-background callback path (line 866) to the background callback path (line 635), ensuring that NoUpdate() is only set when there are actual outputs to update. Fixes plotly#3628
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Summary
When a background callback with no outputs raises an exception, the error handler is called. If the error handler returns
None, the code was incorrectly settingoutput_value = NoUpdate(), which then triggered anInvalidCallbackReturnValueexception at the output validation step.Fix
This change adds the same
output_speccheck that exists in the non-background callback path to the background callback path at_callback.py:635, ensuring thatNoUpdate()is only set when there are actual outputs to update.Testing
The issue includes a minimal reproducible example that can be used to verify the fix.
Related Issue
Fixes #3628