title: Customizing how DataTables displays missing values in Shiny
body: <p><code>DataTables</code>, in Shiny, displays missing values as blank space. Is there a way to change that? I'm dreaming especially of the gray, italicized <em>NA</em>s that RStudio uses in its data viewer. I'd have no problem with injecting such strings into character columns for display purposes, but, of course, sometimes the columns are numeric, or date, and converting them just for display seems problematic.</p>
  
  <p>MWE of DT's default missing values display:</p>
  
  <pre class="lang-r prettyprint-override"><code>library(DT)
  library(shiny)
  
  ui &lt;- fluidPage(
      dataTableOutput("airquality")
  )
  
  server &lt;- function(input, output) {
      output$airquality &lt;- renderDataTable(airquality)
  }
  
  shinyApp(ui = ui, server = server)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/7qJBV.png" rel="noreferrer"><img src="https://i.stack.imgur.com/7qJBV.png" alt="default_dt_display"></a></p>