Changes back default instance properties to null instead of undefined
Changes back default instance properties to null instead of undefined

Previous validations commit should be able to handle this just fine.

As pointed out by @dxg, when data is saved and late fetched, values can
be null, not undefined, so it makes more sense to have them defaulted
to null for consistency.

kolonse/node-orm2,benkitzelman/node-orm2,mariamjpinto/node-orm2,benkitzelman/node-orm2,kapouer/node-orm2,dresende/node-orm2,kapouer/node-orm2,jtrinc/node-orm2,kapouer/node-orm2,ScoutGroup/onionrm,benkitzelman/node-orm2,kolonse/node-orm2,kolonse/node-orm2,stueynz/node-orm2,pskucherov/node-orm2,hallta/node-orm2,locomote/node-orm2