Broken unit test using R-native tree.kernel()

[ArtPoon]

1 Test Suite : 
Kaphi - 39 test functions, 1 error, 0 failures
ERROR in test.kernel.trivial: Error in 2 * V(g1)$bl[n1] : non-numeric argument to binary operator

Using test tree t7:

> require(ape)
> require(igraph)
> t6 <- read.tree(text="((A:3, B:3):7, ((C:2, D:2):5, E:7):3):0;")
> g <- as.igraph(t6)
> edges <- incident_edges(g, 1:9, mode='out')
> edges
$Node1
+ 2/8 edges from 73d4777 (vertex names):
[1] Node1->Node2 Node1->Node3

$Node2
+ 2/8 edges from 73d4777 (vertex names):
[1] Node2->A Node2->B

$A
+ 0/8 edges from 73d4777 (vertex names):

$B
+ 0/8 edges from 73d4777 (vertex names):

$Node3
+ 2/8 edges from 73d4777 (vertex names):
[1] Node3->Node4 Node3->E    

$Node4
+ 2/8 edges from 73d4777 (vertex names):
[1] Node4->C Node4->D

$C
+ 0/8 edges from 73d4777 (vertex names):

$D
+ 0/8 edges from 73d4777 (vertex names):

$E
+ 0/8 edges from 73d4777 (vertex names):
> get.edge.attribute(g, 'length', edges[[1]])
NULL