title: R shiny app errors with ui.R
body: <p>I am aware of the <a href="https://groups.google.com/forum/#!topic/shiny-discuss/-4c2JYYKeAI/discussion" rel="nofollow noreferrer">common mistakes</a> discussion on this topic. I've tried various combinations of adding or deleting IDs, labels, and commas and I can't seem to figure out what is wrong with my code. </p>
  
  <p>Right now my app doesn't do anything substantial, I'm just trying to get it set up. Right now, expected behavior is that it runs, allows the user to enter any text, hit a submit button, and returns "hello world!"</p>
  
  <p>server.R code:</p>
  
  <pre><code>library(shiny)
  shinyServer(   
    function(input, output) {
     output$results &lt;- renderText({
                "hello world!"           
                }) 
    }
  )                               
  </code></pre>
  
  <p>ui.R code:</p>
  
  <pre><code>library(shiny)
  shinyUI(fluidPage(
     titlePanel("Title goes here."),
     sidebarLayout(
        sidebarPanel(
        helpText("Enter a few words, then select 'submit'!"),
        textInput("input"),
        submitButton("submit", label = "submit"),
     ),
  mainPanel(
    textOutput("results")
    )
  )
  ))
  </code></pre>
  
  <p>Actual behavior returns this error on the browser:</p>
  
  <pre><code>ERROR: argument "label" is missing, with no default
  </code></pre>
  
  <p>And this error in the R console:</p>
  
  <pre><code>&gt; shiny::runApp()
  </code></pre>
  
  <blockquote>
  <pre><code>Listening on http://127.0.0.1:4635
  Error in label %AND% tags$label(label, `for` = inputId) : 
    argument "label" is missing, with no default
  Error in label %AND% tags$label(label, `for` = inputId) : 
    argument "label" is missing, with no default
  </code></pre>
  </blockquote>
  
  <p>Any general suggestions for debugging shiny apps will be greatly appreciated!</p>