library(grid)

r1 <- rectGrob(width = unit(0, "npc"), gp = gpar(col = "red", fill = "grey")) # zero-width
r2 <- rectGrob(height = unit(0, "npc"), gp = gpar(col = "red", fill = "grey")) # zero-height

grid.draw(r1) # depicted as a vertical line, rather than disappear completely
grid.draw(r2) # depicted as a horizontal line, rather than disappear completely

p <- ggplot(data, aes(x = value)) +
  geom_histogram(color = "red") +
  facet_wrap(~ key, ncol = 1)

View(layer_data(p) %>% filter(PANEL == 2)) # look at the data associated with facet panel 2

# modified version of StatBin2 inherits from StatBin, except for an
# additional 2nd last line in compute_group() function
StatBin2 <- ggproto(
  "StatBin2",
  StatBin,
  compute_group = function (data, scales, binwidth = NULL, bins = NULL,
                            center = NULL, boundary = NULL,
                            closed = c("right", "left"), pad = FALSE,
                            breaks = NULL, origin = NULL, right = NULL,
                            drop = NULL, width = NULL) {
    if (!is.null(breaks)) {
      if (!scales$x$is_discrete()) {
        breaks <- scales$x$transform(breaks)
      }
      bins <- ggplot2:::bin_breaks(breaks, closed)
    }
    else if (!is.null(binwidth)) {
      if (is.function(binwidth)) {
        binwidth <- binwidth(data$x)
      }
      bins <- ggplot2:::bin_breaks_width(scales$x$dimension(), binwidth,
                                         center = center, boundary = boundary,
                                         closed = closed)
    }
    else {
      bins <- ggplot2:::bin_breaks_bins(scales$x$dimension(), bins,
                                        center = center, boundary = boundary,
                                        closed = closed)
    }
    res <- ggplot2:::bin_vector(data$x, bins, weight = data$weight, pad = pad)

    # drop 0-count bins completely before returning the dataframe
    res <- res[res$count > 0, ]

    res
  })

ggplot(data, aes(x = value)) +
  geom_histogram(color = "red", stat = StatBin2) + # specify stat = StatBin2
  facet_wrap(~ key, ncol = 1)