title: Using shiny modules and shinydashboard: shiny.tag error
body: <p>I'm trying to create and use shiny modules inside a shinydashboard app but I keep getting this error:</p>
  
  <pre><code>Error in FUN(X[[i]], ...) : Expected an object with class 'shiny.tag'.
  </code></pre>
  
  <p>Here is the app as condensed as possible:</p>
  
  <h2>ui.r</h2>
  
  <pre><code>library(shiny)
  library(shinydashboard)
  
  source("modules.r")
  
  ui &lt;- dashboardPage(
   dashboardHeader(
    title = "Shiny modules and shinydashboard"
   ),
  
   dashboardSidebar(
    sidebarMenu(
     menuItem("PointA") 
    )
   ),
  
   dashboardBody(
    tabItems(
     fooUI("myid") 
    )
   )
  )
  </code></pre>
  
  <h2>server.r</h2>
  
  <pre><code>server &lt;- function(input, output) {
   callModule(foo, "myid") 
  }
  </code></pre>
  
  <h2>modules.r</h2>
  
  <pre><code>fooUI &lt;- function(id) {
   ns &lt;- NS(id)
  
   tagList(
    tabItem(
     tabName = "PointA",
     textOutput(ns("text"))
    )
   )
  }
  
  foo &lt;- function(input, output, session){
  
   output$text &lt;- renderText(
    rnorm(1)
   )
  }
  </code></pre>
  
  <p>What am I doing wrong? I got other kinds of modules to work in a "normal" shiny app, however, whenever I try to use a module within shinydashboard it fails.</p>
  
  <p>I am using the newest version of <code>R</code>, <code>shiny</code> and <code>shinydashboard</code>. This is not the issue here.</p>