title: R Shiny Set SelectizeInput default value as NULL
body: <p>I tried to have below code working. But the default value of the selectizeInput widget was not NULL as I expected. Before when I allowed multiple input the default setting was working (as NULL). But I will need a single select input this time. Anyone has suggestions?</p>
  
  <pre><code>       selectizeInput("request","Select Existing Request",
                 choice = unique(fileNames),multiple = FALSE,
                 selected = NULL)
  </code></pre>