How to use renderChart2() when the data file has not been uploaded yet ?

server.R

library(shiny)
library(rCharts)
library(data.table)
####
#### Server
####
shinyServer(function(input, output) {
  ##
  ## load data csv file
  ##
  fileInput <- reactive( {
    if (is.null(input$files)){ # User has not uploaded a file yet
      return(NULL)
    }
    input$files
  })
  ##
  ## output message : file loaded
  ##
  output$loaded <- reactive({
    if (is.null(input$files)){ # User has not uploaded a file yet
      return("no file loaded yet")
    }
    ""
  })
  ##
  ## read data file
  ##
  dataInput <- reactive({
    if (is.null(input$files)){ # User has not uploaded a file yet
       return(NULL) # WHAT COULD WE PUT HERE ??? 
    }
    inFile <- input$files
    read.csv(inFile$datapath, header=T)
  })
  ##
  ## output: print contents of loaded file
  ##
  output$dat <- renderChart2({
    dTable(dataInput())
  })
})

ui.R

library(shiny)
library(rCharts)
library(data.table)
####
#### UI 
####
shinyUI(pageWithSidebar(
  headerPanel("SAP import"),
  ##
  ## sidebar panel
  ##
  sidebarPanel(
    fileInput("files", "File data", multiple=FALSE)         
  ),
  ##
  ## main panel 
  ##
  mainPanel(
    tabsetPanel(
      tabPanel("Data", 
               textOutput("loaded"),
               br(), 
              chartOutput("dat", 'datatables')
      )
    ),id="idtab"
  )
))