Purpose of .nloptr object?

I see this code snippet suggested in the performance vignette:

https://cran.r-project.org/web/packages/lme4/vignettes/lmerperf.html

nlopt <- function(par, fn, lower, upper, control) {
    *.nloptr <<-* res <- nloptr(par, fn, lb = lower, ub = upper,
        opts = list(algorithm = "NLOPT_LN_BOBYQA", print_level = 1,
        maxeval = 1000, xtol_abs = 1e-6, ftol_abs = 1e-6))
    list(par = res$solution,
         fval = res$objective,
         conv = if (res$status > 0) 0 else res$status,
         message = res$message
    )
}

That's writing an .nloptr object to .GlobalEnv (usually), but there's no
mention of why and I don't see any usage of this object anywhere else in
the code base:

grep -Fr ".nloptr" lme4/R

Am I missing something?
Mike C