Test behaviour with missing values, e.g. in year

[maurolepore]

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Can you provide something like this?

#' A title line, for example: Sum two numbers
#' 
#' One description paragraph. For example: This function sums two numbers. It
#' does nothing really useful other than showing how to document a function.
#'
#' Optionally, any number of paragraphs giving details. We follow the tidyverse
#' style guide: <https://style.tidyverse.org/>.
#' 
#' @param x Definition of the `x` argument. For example: A number.
#' @param y Definition of the `y` argument. For example: A number.
#'
#' @return What do you expect this function to return? For example: A number.
#' @export
#'
#' @examples
#' sum_two_numbers(1, 1)
sum_two_numbers <- function(x, y) {
  stopifnot(is.numeric(x), is.numeric(y))
  
  x + y
}

[maurolepore]

Duplicates #326