title: Force no default selection in selectInput()
body: <p>The Shiny <a href="http://cran.r-project.org/web/packages/shiny/shiny.pdf" rel="noreferrer">documentation</a> mentions that for <code>selectInput()</code>: </p>
  
  <blockquote>
    <p><code>selected</code> The value (or, if none was supplied, the title) of the navigation item that should be selected by default. If NULL, the ﬁrst navigation will be selected. </p>
  </blockquote>
  
  <p>What if by default I don't want to select any value from select list? </p>
  
  <p>Actually my select value is getting selected by default and rest part of app is getting executed automatically. But I don't want to select any value initially. What should I supply to the <code>selected</code> argument in <code>selectInput()</code> to do that?</p>
  
  <hr>
  
  <p>Indeed, I don't want anything to be selected automatically. I used the code below but still it's selecting first available value from the list. I want there to be no selection by default, so the user can then select any option.</p>
  
  <pre><code>output$Choose_App &lt;- renderUI({
  selectInput("app",
              "Select App:",
              choices = as.character(mtrl_name),
              selected = NULL ,
              multiple = FALSE
             )
          })
  </code></pre>
  
  <hr>
  
  <p>Going through the <a href="http://cran.r-project.org/web/packages/shiny/shiny.pdf" rel="noreferrer">documentation</a>  I noticed that the selection can be empty only if I select <code>multiple=TRUE</code>. Is this correct? </p>
  
  <p>When I changed to <code>multiple=TRUE</code>, then it it's not getting selected by default, which is what I want. But unfortunately before making any selection I am also getting following error message: </p>
  
  <pre><code>ERROR: bad 'file' argument 
  </code></pre>
  
  <p>Does anybody know about this if I am doing something wrong? But if I select this file then error is gone.</p>
  
  <p><img src="https://i.stack.imgur.com/Z5jq7.png" alt="enter image description here"></p>
  
  <p>I am using following code for this:</p>
  
  <pre><code># server.R
  setwd("/opt/shiny-server/samples/sample-apps/P-Dict_RDS2")
  mtrl_name &lt;- try(system("ls | grep -i .rds", intern = TRUE))
  
  shinyServer(function(input, output) {
  
  # First UI input (Service column) filter clientData 
  output$Choose_Molecule &lt;- renderUI({
  selectInput("molecule",
              "Select Molecule:",
              choices = as.character(mtrl_name),
              selected = input$molecule,
              multiple = TRUE
             )
          })
  </code></pre>