滑块输入日期，非数字到二进制

我正在尝试在R Shiny的这些日期之间创建一个sliderinput。每次，我都会收到此错误： 警告：错误：-：二进制运算符的非数字参数   [没有可用的堆栈跟踪]

and this as output in the app, instead of the slider: non-numeric argument to binary operator

Yet, I have seen countless examples of this (i.e https://github.com/eparker12/nCoV_tracker/blob/master/app.R) , so I do not see why this does not work. I have the libraries Lubridate, Shiny and ShinyWidgets and have updated them to the latest versions.

ui=fluidPage(
  uiOutput("plot_date_page1"),
)

server=function(input,output,session){

output$plot_date_page1<-renderUI({
    sliderInput("plot_date_page1","Date",
                label = h5("Select mapping date"),
                min = as.Date("1980-01-01","%Y-%m-%d"),
                max = as.Date("2020-01-01","%Y-%m-%d"),
                value = as.Date("2020-01-01"),
                timeFormat = "%y %b")
        })

}

shinyApp(ui = ui, server = server)