title: Scatterplot without any values in both variables or in one of them
body: <p>As the title says, I want to see the empty plot with the coordinate system and the axis even if there are no values available. </p>
  
  <p>So far I get an error for those smoothScatter-functions, that do not contain values.</p>
  
  <pre><code>    a1 &lt;- subset(a, datasource == 1)
      a2 &lt;- subset(a, datasource == 2)
      a3 &lt;- subset(a, datasource == 3)
      a4 &lt;- subset(a, datasource == 4)
      a5 &lt;- subset(a, datasource == 5)
      a6 &lt;- subset(a, datasource == 6)
      a7 &lt;- subset(a, datasource == 7)
      par(mfrow=c(3,3))
      smoothScatter(a$profiledepth, a$horizondepth_lower, nbin=256, nrpoints=0, ylim=c(0,520), xlim=c(0,520), main='Alle', ylab='Tiefe der Horizontuntergrenze / cm', xlab='Profiltiefe / cm')
      smoothScatter(a1$profiledepth, a1$horizondepth_lower, nbin=256, nrpoints=0, ylim=c(0,520), xlim=c(0,520), main='Alle', ylab='Tiefe der Horizontuntergrenze / cm', xlab='Profiltiefe / cm')
      smoothScatter(a2$profiledepth, a2$horizondepth_lower, nbin=256, nrpoints=0, ylim=c(0,520), xlim=c(0,520), main='Alle', ylab='Tiefe der Horizontuntergrenze / cm', xlab='Profiltiefe / cm')
      smoothScatter(a3$profiledepth, a3$horizondepth_lower, nbin=256, nrpoints=0, ylim=c(0,520), xlim=c(0,520), main='Alle', ylab='Tiefe der Horizontuntergrenze / cm', xlab='Profiltiefe / cm')
      smoothScatter(a4$profiledepth, a4$horizondepth_lower, nbin=256, nrpoints=0, ylim=c(0,520), xlim=c(0,520), main='Alle', ylab='Tiefe der Horizontuntergrenze / cm', xlab='Profiltiefe / cm')
      smoothScatter(a5$profiledepth, a5$horizondepth_lower, nbin=256, nrpoints=0, ylim=c(0,520), xlim=c(0,520), main='Alle', ylab='Tiefe der Horizontuntergrenze / cm', xlab='Profiltiefe / cm')
      smoothScatter(a6$profiledepth, a6$horizondepth_lower, nbin=256, nrpoints=0, ylim=c(0,520), xlim=c(0,520), main='Alle', ylab='Tiefe der Horizontuntergrenze / cm', xlab='Profiltiefe / cm')
      smoothScatter(a7$profiledepth, a7$horizondepth_lower, nbin=256, nrpoints=0, ylim=c(0,520), xlim=c(0,520), main='Alle', ylab='Tiefe der Horizontuntergrenze / cm', xlab='Profiltiefe / cm')
  </code></pre>
  
  <p>Any ideas how to solve it?</p>