graphml `edgedefault` not handled to spec

[Sébastien Heymann]

from http://graphml.graphdrawing.org/primer/graphml-primer.html#GraphGraph

 Graphs in GraphML are mixed, in other words, they can contain directed
 and undirected edges at the same time. If no direction is specified
 when an edge is declared, the default direction is applied to the edge.
 The default direction is declared as the XML Attribute edgedefault of
 the graph element. The two possible value for this XML Attribute are
 directed and undirected. Note that the default direction must be
 specified.

However, when specifying an edgedefault Gephi complains "Edge type doesn't
fit with default".

More importantly having a graph with `edgedefault="undirected"` but all edges
but one with `directed="true"` makes the unspecified edge directed as well. My
work around for now is to just not specify edgedefault for the graph, and manually
specifying `directed` as `true` or `false` for each edge - even though this doesn't
strictly follow the GraphML spec.

[Sébastien Heymann (sebastien.heymann)]

The issue doesn't seem to come from the importer itself but the ImportContainerImpl.addEdge().

I don't understand the code from lines 208 to 224, which raise this exception when an edge has a different type than the default type.