title: Graphic not appearing in R: null device?
body: <p>I'm trying to produce a graphic using rworldmap, using my data frame dagg. 
  ETA: <a href="https://github.com/pourque/country-data/blob/master/data/dagg.csv" rel="noreferrer">data</a>.
  Here's what I have so far.</p>
  
  <pre><code>library(rworldmap)
  data(dagg)
  sPDF &lt;- joinCountryData2Map(dagg, joinCode='ISO2',
  nameJoinColumn='country', verbose='TRUE')
  
  mapDevice()
  
  mapCountryData(sPDF, nameColumnToPlot='avoidance', 
  numCats=10, mapTitle="Avoidance", addLegend=TRUE)
  dev.off()
  </code></pre>
  
  <p>But when I run, nothing shows up. The console displays "null device 1". It was working just now, and I'm not sure what could have changed it...</p>
  
  <p>Perhaps I'm not using the right <a href="https://stackoverflow.com/questions/8321756/what-is-a-null-graphics-device/8322743">device</a>?</p>
  
  <p>ETA: <a href="http://cran.r-project.org/web/packages/rworldmap/vignettes/rworldmap.pdf" rel="noreferrer">Here's</a> the rundown on rworldmap that I'm reading from.</p>