如何解决此错误：“错误：缺少参数，没有默认值”

Question

library(shiny)

shinyUI(fluidPage(

  titlePanel(title = "stat project"),
  sidebarLayout(
    sidebarPanel(
       selectInput("x","select option", 
                   choices=DataTables_example_File_export$`DataTables example - File export`),

    ),


    mainPanel(
       tabeloutput("DataTables_example_File_export")


              ) 
      )
    )
)