R session quits when the number of strata < 10

[jialul]

I am using wfe version 1.9.1 and found that the current version of the package does not allow the number of strata to be less than 10 while also printing the helping message ("verbose = TRUE"). With N < 10 and verbose = TRUE, the R session will automatically exit. But if we do not print the helping message ("verbose = FALSE"), the package works fine. To reproduce the error, I use the original sample code from the package and changed the number of distinct units from 10 to 7. All the other parts stay the same as the original sample code.

My hunch is that the sudden exit of R session is cased by these few lines in C which relates to "verbose" but I could be wrong. https://github.com/insongkim/wfe/blob/d7c0b7668a3cb62bbd0b048667924f8e4df75449/src/wfe.c#L1060-L1067

N <- 7 # number of distinct units 
Time <- 20 # number of distinct time
beta <- 1
treat <- matrix(rbinom(N*Time, size = 1, 0.25), ncol = N)
while ((sum(apply(treat, 2, mean) == 0) > 0) | (sum(apply(treat, 2, mean) == 1) > 0) |
       (sum(apply(treat, 1, mean) == 0) > 0) | (sum(apply(treat, 1, mean) == 1) > 0)) {
  treat <- matrix(rbinom(N*Time, size = 1, 0.25), ncol = N)
}
treat.vec <- c(treat)
alphai <- rnorm(N, mean = apply(treat, 2, mean))
x1 <- matrix(rnorm(N*Time, 0.5,1), ncol=N)
x2 <- matrix(rbeta(N*Time, 5,1), ncol=N)
x1.vec <- c(x1)
x2.vec <- c(x2)
y <- matrix(NA, ncol = N, nrow = Time)
for (i in 1:N) {
    y[, i] <- alphai[i] + treat[, i] + x1[,i] + x2[,i] + rnorm(Time)
}
y.vec <- c(y)
unit.index <- rep(1:N, each = Time)
time.index <- rep(1:Time, N)
Data.str <- as.data.frame(cbind(y.vec, treat.vec, unit.index, x1.vec, x2.vec))
colnames(Data.str) <- c("y", "tr", "strata.id", "x1", "x2")
Data.obs <- as.data.frame(cbind(y.vec, treat.vec, unit.index, time.index, x1.vec, x2.vec))
colnames(Data.obs) <- c("y", "tr", "unit", "time", "x1", "x2")

library(wfe)
mod.ate <- wfe(y~ tr+x1+x2, data = Data.str, treat = "tr",
               unit.index = "strata.id", method = "unit",
               qoi = "ate", hetero.se=TRUE, auto.se=TRUE)
summary(mod.ate)