Problem with starting shiny: argument "func" is missing

[Statistikfrosch]

Hi there,
I'm just starting my very first basic steps with shiny. When I click on "Run App", the output-window opens for 1 sec, then it's gone and I get error messages in "shinyServer" (argument "func" is missing"). Do you have an idea whats wrong?
Thanks a lot,
Roman

**Error message:**
Listening on http://127.0.0.1:6078
Warning: Error in shinyServer: argument "func" is missing, with no default
  50: shinyServer
Error in shinyServer() : argument "func" is missing, with no default

My ui.R - Code:

library(shiny)
library(shinydashboard)
setwd("C:/Users/[...]/ShinyTEST/firstShinyApp")

shinyUI(
  dashboardPage(
    dashboardHeader(title = "This is the header"),
    dashboardSidebar(
      menuItem("Dashboard"),
        menuSubItem("Dashboard Finance"),
        menuSubItem("Dashboard Sales"),
      menuItem("Detailded Analysis"),
      menuItem("Raw Data")
    ),
    dashboardBody()
  )
)