Server Crashing at GET->'api/skribbl' with unknown ID

[tcandens]

It will not crash if id cannot be cast to Mongo ObjectId, but it is crashing for me if the ID is the correct length but does not exist in the database.

/home/joey/Codefellows/exquisite/lib/tree3_by_id.js:13
  Skribbl.find({ parent_skribbl: topParent._id }, function( err, first_childre
                                          ^
TypeError: Cannot read property '_id' of null
    at buildTree (/home/joey/Codefellows/exquisite/lib/tree3_by_id.js:13:43)
    at /home/joey/Codefellows/exquisite/routes/skribbl_routes.js:62:7
    at /home/joey/Codefellows/exquisite/node_modules/mongoose/lib/query.js:1173:16
    at /home/joey/Codefellows/exquisite/node_modules/mongoose/node_modules/kareem/index.js:109:16
    at process._tickDomainCallback (node.js:486:13)
21 May 11:13:35 - [nodemon] app crashed - waiting for file changes before starting...

Is any body else able to replicate?