Check for existance of TreeAttribute

I got a NullRef on this line: new Tuple<Type, TreeAttribute>(x, x.GetCustomAttributes<TreeAttribute>(false).Single())

x.GetCustomAttributes<TreeAttribute>(false) returned no elements for the assembly DictionaryFix.dll (http://our.umbraco.org/projects/backoffice-extensions/digibiz-dictionary-section)

Ps. Sorry about the name of the branch (patch-1), I haven't got a clue where to rename it...