r - Error in dev.off() : cannot shut down device 1 (the null device)

Question

I am new to R programming and I got hit with this error when I tried to run the code. This simply creates a pie chart with some data. Can anyone explain to me why I am getting this error and what it means?

1) I am running windows 2) Version 3.4.0 3) I am using RGui desktop 4) R version 3.4.0

# Create data for the graph.
x <- c(21, 62, 10, 53)
labels <- c("London", "New York", "Singapore", "Mumbai")

# Give the chart file a name.
png(file = "city_title_colours.jpg")

# Plot the chart with title and rainbow color pallet.
pie(x, labels, main = "City pie chart", col = rainbow(length(x)))

# Save the file.
dev.off()

Answer 1

try

while (!is.null(dev.list()))  dev.off()