set could allow empty input without warning

[jangorecki]

d = data.table(a=1, b=1)
dropcols = character()
set(d, NULL, dropcols, NULL)
#Warning message:
#In set(d, NULL, dropcols, NULL) :
#  length(LHS)==0; no columns to delete or assign RHS to.

I don't think we really need a warning here, it could work without the need for if (length(dropcols)) set(...).

[jangorecki]

data.table/src/assign.c

Lines 346 to 347 in 6f17d18

	if (!length(cols)) {
	warning("length(LHS)==0; no columns to delete or assign RHS to."); // test 1295 covers

That would unfortunately also remove the warning from d[, character() := NULL]. Are we OK to remove the warning from there also? IMO make sense

[MichaelChirico]

Agree don't need to warn, verbose message would be fine