the NA argument in fifelse should support vector

[shrektan]

data.table::fifelse(c(T, F, NA, T, F, NA), 1:6, 11:16, 101:106)
# Error in data.table::fifelse(c(T, F, NA, T, F, NA), 1:6, 11:16, 101:106) : 
#  Length of 'na' is 6 but must be 1