title: Error when making a simple boxplot with ggplot2
body: <p>Using the mpg data in R, I can make a boxplot of 'displ' with</p>
  
  <pre><code>boxplot(mpg$displ)
  </code></pre>
  
  <p>But when I try to make this simple boxplot with ggplot, </p>
  
  <pre><code>ggplot(data = mpg, aes(displ)) + geom_boxplot()
  </code></pre>
  
  <p>I get this error;</p>
  
  <pre><code>Error in seq.default(from = best$lmin, to = best$lmax, by = best$lstep) : 'from' must be of length 1
  In addition: Warning messages:
  1: Continuous x aesthetic -- did you forget aes(group=...)? 
  2: In is.na(data$y) :  is.na() applied to non-(list or vector) of type 'NULL'
  </code></pre>