[igraph] Help with bipartite.projection()

[capitano . nemo]

Hello list,

I have a bipartite graph "igraph_bi" with two types of nodes defined as

> table(V(igraph_bi)$type)

thread   user
 75438  79174

Now when I try to call bipartite.projection(igraph_bi) I get

Error in bipartite.projection(igraph_bi) :
  `NA' is not allowed in vertex types
In addition: Warning message:
In bipartite.projection(igraph_bi) : vertex types converted to logical

I am not sure to understand why the function is expecting a logical, but 
still it is trying to convert V(igraph)$type into logical (here the 
function: 
https://git.huit.harvard.edu/igraph/igraph/blobs/eb91caf3f811d5ddcd89bd238c501c39a2124b73/interfaces/R/igraph/R/bipartite.R).

Should I convert my $type vector to TRUE/FALSE before converting?

Also why does the function expect a logical?

Thanks