When collection::drop() is invoked on a collection that does not exist, it is inconsistent about whether or not it throws operation_exception. Currently, it varies between server type and server version (an exception is not thrown when connected to mongod 3.2 or later or when connected to mongos, but an exception is thrown when connected to mongod versions 3.0 or earlier).

collection::drop() should never throw an exception due to a missing collection.