improve paste_with_na()

#' @noRd

paste_with_na <- function(...,

                          sep = "",

                          collapse = NULL,

                          recycle0 = FALSE) {

                          collapse = NULL) {

  ll <- list(...)

  if(length(ll) == 0) {

    return(character(0))

  }

  n <- max(vapply(ll, length, numeric(1)))

  ll <- lapply(ll, function(.x) {

    if(length(.x) < n) {

      .x <- rep_len(.x, n)

    }

    .x[is.na(.x)] <- ""

    .x

  })

  ll$sep <- sep

  ll$collapse <- collapse

  ll$recycle0 <- recycle0

  do.call("paste", ll)

  ll <- lapply(ll, function(.x) {rep_len(.x, n)})

  out <- character(length = n)

  for (ii in seq_len(n)) {

    ele <- lapply(ll, `[`, ii)

    if (all(is.na(unlist(ele)))) {

      out[ii] <- NA

    } else {

      id <- vapply(ele, is.na, logical(1))

      ele <- ele[!id]

      ele$sep <- sep

      out[ii] <- do.call("paste", ele)

    }

  }

  if (is.null(collapse)) {

    out <- ifelse(is.na(out), "", out)

  } else {

    if (length(out) > 1) {

      if (all(is.na(out))) {

        out <- ""

      } else {

        out <- paste(out[!is.na(out)], collapse = collapse)

      }

    } else {

      out <- if (is.na(out)) "" else out

    }

  }

  out

}