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fix: handle None return from error handler in no-output background callbacks #4012

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fix: handle None return from error handler in no-output background callbacks #4012

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cce590e
fix: handle None return from error handler in no-output background ca…
dajiaohuang Sep 25, 2026
ad21a5b
Merge branch 'dev' into fix/3628-background-callback-error-handler
dajiaohuang Sep 25, 2026
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9 changes: 6 additions & 3 deletions dash/_callback.py
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Original file line number Diff line number Diff line change
Expand Up @@ -635,6 +635,7 @@ def _update_background_callback(
kwargs,
background,
multi,
output_spec,
cache_key=None,
job_id=None,
):
Expand Down Expand Up @@ -663,6 +664,7 @@ def _update_background_callback(
error_handler,
callback_ctx,
multi,
output_spec,
cache_key=cache_key,
job_id=job_id,
)
Expand All @@ -675,6 +677,7 @@ def _handle_rest_background_callback(
error_handler,
callback_ctx,
multi,
output_spec,
has_update=False,
cache_key=None,
job_id=None,
Expand All @@ -693,7 +696,7 @@ def _handle_rest_background_callback(
if error_handler:
output_value = error_handler(exc)

if output_value is None:
if output_value is None and output_spec:
output_value = NoUpdate()
# set_props from the error handler uses the original ctx
# instead of manager.get_updated_props since it runs in the
Expand Down Expand Up @@ -927,7 +930,7 @@ def add_context(*args, **kwargs):
)

output_value, has_update, skip = _update_background_callback(
error_handler, callback_ctx, response, kwargs, background, multi
error_handler, callback_ctx, response, kwargs, background, multi, output_spec
)
if skip:
return output_value
Expand Down Expand Up @@ -998,7 +1001,7 @@ async def async_add_context(*args, **kwargs):
callback_ctx,
)
output_value, has_update, skip = _update_background_callback(
error_handler, callback_ctx, response, kwargs, background, multi
error_handler, callback_ctx, response, kwargs, background, multi, output_spec
)
if skip:
return output_value
Expand Down
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