title: R igraph write.graph() edgelist if graph is empty
body: <p>Using in R the package 'igraph' and calling the function:</p>
  
  <pre><code>graph &lt;- graph.empty(10,directed=FALSE)
  write.graph(graph,"some/path/graph.txt",format="edgelist")
  </code></pre>
  
  <p>If I recall the graph by using</p>
  
  <pre><code>g &lt;- as.undirected(read.graph("some/path/graph.txt",format="edgelist"))
  </code></pre>
  
  <p>the graph is empty but has also NO vertices!</p>