Is there an R function to fill empty nodes?

I'm trying to scrape IMDB website using CSS selector and xpath. For some film there are missing data, therefore it is not possible to create a dataframe.

I would like to find a solution in order to fill empty nodes with Na. I thought to use the content variable to count film (it contains all the other variables) and then if there is an information that I need (suppose metadata) find a way to write the information, otherwise make R write Na.

    content <-         function(url){
                  url %>% read_html() %>% 
                    html_nodes(".lister-item-content")%>% 
                    html_text() 

                })


   metascore <-      function(url){
                  url %>% read_html() %>% 
                    html_nodes("span.metascore") %>% 
                    html_text()
                })

Do you have any suggestion?