In rare situation when a connection may be null we get this stack

TypeError: Cannot call method 'isCompatible' of null

• • [out :: ] at __executeInsertCommand (/home/codez/node_modules/harmony/node_modules/mongodb-mapper/node_modules/mongodb/lib/mongodb/db.js:1868:18)

https://github.com/mongodb/node-mongodb-native/blob/master/lib/mongodb/db.js#L1868

connection is check to be null later in the __executeInsertCommand function.
That check should move up.