> db.data.update({\'name\': \'zero\'}, {\'$set\': {\'value\': 0}}) > db.data.findOne({\'name\': \'zero}) {\'name\': \'zero\', \'value\': 0.0}
A slightly simpler syntax (in Robomongo at least) worked for me:
db.database.save({ Year : NumberInt(2015) });