Rickshaw chart error in Shiny

app.css

.chart_container {
  position: relative;
  display: inline-block;
  font-family: Arial, Helvetica, sans-serif;
}
.rChart {
  display: inline-block;
  margin-left: 40px;
}
.yAxis {
  position: absolute;
  top: 0;
  bottom: 0;
  width: 40px;
}
.legend {
  position: absolute;
  top: 0;
  right: -160px;
  vertical-align: top;
}
.slider {
  margin-left: 40px;
  margin-top: 12px;
}

server.R

require(shiny)
require(rCharts)

inputChoices <- c("A", "B", "C", "D")

shinyServer(function(input, output, session){
  	
  	input2Choices <- reactive({
  		inputChoices[-grep(input$input1, inputChoices)]
  	})

  	output$input1 <- renderUI({
  		selectInput("input1", "Input 1:", choices=as.list(inputChoices))
  	})

  	output$input2 <- renderUI({
  		if(is.null(input$input1))
  			return()
  		selectInput("input2", "Input 2:", choices=input2Choices())
  	})
  	
  carrierInput1 <- reactive({
    switch(input$input1,
           "A" = 1,
           "B" = 2,
           "C" = 3,
           "D" = 4)
    })

    carrierInput2 <- reactive({
    if(is.null(input$input2))
      return()
    if(input$input1 != input$input2){
      return()
    }
    switch(input$input2,
           "A" = 1,
           "B" = 2,
           "C" = 3,
           "D" = 4)
    })

    getData <- function(){
      return(carrierInput2())
    }

  output$mychart = renderChart2({
    z<-getData()
    if(is.null(input$input1))
        return()
    usp = reshape2::melt(USPersonalExpenditure)
    p4 <- Rickshaw$new()
    p4$layer(value ~ Var2, group = 'Var1', data = usp, type = 'area')
    p4$set(width = 600, slider = TRUE)
    #return(p4)
    p4
  })

  	# output$show <- renderPrint({
  	# 	if(is.null(input$input1))
  	# 		return()
  	# 	 print(carrierInput1())
  	# })

   output$show2 <- renderPrint({
    if(is.null(input$input2)){
      return()
    } 
    if(input$input1 == input$input2){
      return()
    }
    #print(carrierInput2())
		Sys.sleep(2)
  })


})

ui.R

require(shiny)
require(rCharts)
shinyUI(pageWithSidebar(
  headerPanel("Dynamic UI inputs with Shiny"),
  sidebarPanel(
    includeCSS('app.css'),
    uiOutput('input1'),
    uiOutput('input2')
  ),
  mainPanel(
   showOutput("mychart", "rickshaw")
 #  verbatimTextOutput("show2")
  )
))

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