title: map sending back an active reactive error
body: <p>Putting together a map on Shiny, but keep running into an error. When I use the same steps using Leaflet, it runs fine, but when I use mapview, it does not. Unfortunately, I can't provide the data for a reproducible example, seeing as it involves a shaping file with length geometry.</p>
  
  <pre><code>library(sf)
  library(shiny)
  library(shinyWidgets)
  library(dplyr)
  library(leaflet)
  library(mapdeck)
  
  ui &lt;- fluidPage(
    fluidRow(
      column(
        width = 10, offset = 1,
        tags$h3("Select Area"),
        panel(
          selectizeGroupUI(
            id = "my-filters",
            params = list(
              state = list(inputId = "state", title = "state:"),
              city = list(inputId = "city", title = "city:"),
              turf = list(inputId = "turf", title = "turf:")
            ))
        ),
        mapviewOutput(outputId = "mymap")
      )
    )
  )
  
  server &lt;- function(input, output, session) {
  
    res_mod &lt;- callModule(
      module = selectizeGroupServer,
      id = "my-filters",
      data = df,
      vars = c("state", "city", "turf")
    )
  
    output$box &lt;- mapview::renderMapview({
  
      res &lt;- res_mod()
  
      mapView(res)
  
    })
  
  }
  
  shinyApp(ui, server)
  </code></pre>
  
  <p>Whenever I run it, I get stuck with the following error:</p>
  
  <pre><code>Warning: Error in .getReactiveEnvironment()$currentContext: Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)
    63: stop
    62: .getReactiveEnvironment()$currentContext
    61: getCurrentContext
    60: .dependents$register
    59: cheat
    52: server [#23]
  </code></pre>