> DT = data.table(A=LETTERS[1:5])
> DT[ A %in% c("C","E"), val:=42][]
A val
<char> <num>
1: A NA
2: B NA
3: C 42
4: D NA
5: E 42
> DT[ A %in% c("C","E"), val:=42, fill=0][] # current behaviour
Error in `[.data.table`(DT, A %in% c("C", "E"), `:=`(val, 42), fill = 0) :
unused argument (fill = 0)
> DT[ A %in% c("C","E"), val:=42, fill=0][] # desired behaviour
A val
<char> <num>
1: A 0
2: B 0
3: C 42
4: D 0
5: E 42
