recmap shiny application - Warning: Error in :: argument of length 0

[cpanse]

> library(shiny)
> recmap_shiny <- system.file('shiny-examples', package = 'recmap')
> shiny::runApp(recmap_shiny, display.mode = 'normal')

Listening on http://127.0.0.1:6832
Loading required package: GA
Loading required package: foreach
Loading required package: iterators
  ____    _    
 / ___|  / \     Genetic 
| |  _  / _ \    Algorithms
| |_| |/ ___ \   
 \____/_/   \_\  version 3.1.1
Type 'citation("GA")' for citing this R package in publications.
Loading required package: Rcpp
Loading required package: sp
Package 'recmap' version 1.0.1
Warning: Error in :: argument of length 0
  133: combn
  131: checkerboard
  130: <reactive:Map> [/Library/Frameworks/R.framework/Versions/3.5/Resources/library/recmap/shiny-examples/server.R#131]
  114: Map
  113: <reactive:Cartogram> [/Library/Frameworks/R.framework/Versions/3.5/Resources/library/recmap/shiny-examples/server.R#168]
   97: Cartogram
   96: renderText [/Library/Frameworks/R.framework/Versions/3.5/Resources/library/recmap/shiny-examples/server.R#57]
   95: func
   82: origRenderFunc
   81: output$plot_hoverinfo
    1: shiny::runApp
Warning: Error in :: argument of length 0
  170: <Anonymous>
Warning: Error in :: argument of length 0
  170: <Anonymous>