Resolving "Warning in if (stri_startswith_fixed(body, "{")) { :..." when using the plumber library in R

Currently getting this error when I make a POST request in plumber:

Warning in if (stri_startswith_fixed(body, "{")) { :
  the condition has length > 1 and only the first element will be used
Warning in if (stri_startswith_fixed(qs, "?")) { :
  the condition has length > 1 and only the first element will be used

This is what my function looks like:

#' Get results from Two Sample t-test
#' @serializer unboxedJSON
#' @param group:character The group col you would like to group data by
#' @param variable:character The variable you would like to be compared between groups
#' @post /twosamplettest/<group>/<variable>
function(req, group, variable) {
    data_as_df <- fromJSON(req$postBody)

    results <- t.test(get(variable) ~ get(group), data=data_as_df)

    group_mean_df <- extractGroupsAndMeansFromTTestResults(results)

    test_results <- list(pvalue=results$p.value, group_stats=as.data.frame(group_mean_df)))

    test_results
}

The request gets a valid response and everything is all good except for that ugly warning message that shows up in the console for every request made.

Any ideas on how to resolve it?