labs should ignore trailing comma

[bersbersbers]

Many ggplot2 functions accept (that is, ignore) a trailing comma. A few don't, such as ggplot::labs:

df <- data.frame()
ggplot2::ggplot(
    df,
    ggplot2::aes(
        x = x,
        y = y, # trailing comma
    ), # trailing comma
) +
    ggplot2::labs(
        x = "x",
        y = "y", # no trailing comma allowed. Error: Argument 3 is empty
    ) +
    ggplot2::theme(
        , # trailing comma
    )

[bersbersbers]

Also, ggplot2::guides.

[yutannihilation]

Thanks for reporting. I'm not sure if we need consistency here, but these two seems easy.