::: {.cell hash='02_R_introduction_cache/pdf/unnamed-chunk-36_e0f58f428fa6862a402ec22235f9104a'}

```{.r .cell-code}
b <- "this variable has a value"
is.na(b)
```

::: {.cell-output .cell-output-stdout}
```
[1] FALSE
```
:::
:::