This is a LOT of code to expect someone to sift through. Do you even know which of your 3 calls to Tree::Nary->find() causes the error? All I can offer is some generic debugging techniques:

• Re-read some of the advice to use other modules in Tree::Nary n00b has questions.
• Take some time to reduce your code to less than 20 lines, while still getting the same error. This may take some hand-crafting of small input data.
• use Data::Dumper; print Dumper(); often
• Look at the source code for Tree::Nary to figure out what Tree::Nary->find() expects as arguments, if the documentation is not clear.
• Super Search on "Tree::Nary" to see if anything pops up.