Sorry for the enormously late reply. Wouldn’t if (is.null(line)) line <- ''work better? That way I’d assume you’d get a list of defined variables or so instead of nothing …

Done, though I don't think that this would be the intended course of action for most cases. Currently it predominantly arises due to a race condition after notebook having changed its structure, as in the standard notebook implementation Tab on an empty cell just gives you an indent (rather than a completion) - so returning a list of all completions did not seem important to me. But I am happy with propose solution as well (now comitted), I can see that it could be useful in certain cases.

OK!, thank you for your PR!

hello, i'm stupid and can you tell me how to use
the "Re-assign null line to empty string" ? is run it in jupyterlab'R every time when i want use R in jupyterlab? Thanks