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

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

T4rk1n merged 11 commits into

plotly:devplotly/dash:devfrom

dajiaohuang:fix/3628-background-callback-error-handlerdajiaohuang/dash:fix/3628-background-callback-error-handlerCopy head branch name to clipboard