problem joining with character(0)

[tvr101]

I recently upgraded to 1.9.2 and encountered the following issue. Previously this returned an empty data.table as I had expected (and desired), but now returns an error:

x <- data.table(a=character(0), b=character(0), c=numeric(0))
setkey(x, a, b)

x[J("foo", character(0)), nomatch=0]
Error in if (mn%%n[i] != 0) warning("Item ", i, " is of size ", n[i],  : 
  missing value where TRUE/FALSE needed

x[J(character(0), "foo"),nomatch=0]
Error in if (mn%%n[i] != 0) warning("Item ", i, " is of size ", n[i],  : 
  missing value where TRUE/FALSE needed

if there is only one key then this seems to behave as before

x <- data.table(a=character(0), b=character(0), c=numeric(0))
setkey(x, a)
x[J(character(0)),nomatch=0]
Empty data.table (0 rows) of 3 cols: a,b,c

is this expected with the new release? in my actual usage character(0) is a value held by another variable and that variable is used to search inside the data.table - is it user's responsibility to now check and avoid searching with empty character vectors?