diff --git a/strings.qmd b/strings.qmd
index 7ac48e7..01b089f 100644
--- a/strings.qmd
+++ b/strings.qmd
@@ -3,6 +3,7 @@
 ```{r}
 #| results: "asis"
 #| echo: false
+
 source("_common.R")
 status("complete")
 ```
@@ -166,7 +167,7 @@ str_c("Hello ", c("John", "Susan"))
 `str_c()` is very similar to the base `paste0()`, but is designed to be used with `mutate()` by obeying the usual tidyverse rules for recycling and propagating missing values:
 
 ```{r}
-df <- tibble(name = c("Flora", "David", "Terra"))
+df <- tibble(name = c("Flora", "David", "Terra", NA))
 df |> mutate(greeting = str_c("Hi ", name, "!"))
 ```