Null checkboxes in Shiny

This was an idea I had

ui <- fluidPage(
  checkboxGroupInput(
    "checks",
    "Check boxes",
    choices = month.name,
    selected = month.name[1]
  ),
  actionButton("search", "Search"),
  uiOutput("ui_stuff")
)

server <- function(input, output, session) {
  reactive_checkboxes <- reactiveValues(checks = c())

  observeEvent(input$checks, {
    print("change")

    reactive_checkboxes$checks <- input$checks
  })

  observeEvent(input$search, {
    if (is.null(input$checks)) {
      showModal(modalDialog(
        title = "Invalid search conditions!",
        div(p("You must select at least one theme to filter the data."),
            p("Click dismiss and your previously selected set of themes will be re-selected.")
      )))
      
      updateCheckboxGroupInput(session,
                               "checks",
                               selected = reactive_checkboxes$checks)
      
    }
  })


  output$ui_stuff <- renderUI({
    "dummy element here"
  })
}


shinyApp(ui, server)