NSManagedObjectContext is not saving the NSManagedObject Values in SWIFT 3.0 and XCOde 8 - swift3

Question

I am facing a problem while saving the NSManagedObject to NSManagedObjectContext in Swift 3.0 and Xcode 8. Adding the code snippets for better Understanding
let config = NSManagedObject(entity: entityDescription!, insertInto: self.moc) as! Config
Here Config class is derived from NSManagedObject
class Config: NSManagedObject {
// Insert code here to add functionality to your managed object subclass
}
Assigning the Key and value to my config as below and calling a save
config.key = "access_token"
config.value = access_token
do
{
try config.managedObjectContext?.save()
}catch let error as NSError
{
NSLog(error.localizedDescription)
onCompletion("Login Failed")
return
}
This doesnt throw any error to me, but while fetching the value of access_token from NSManagedObject, value is nil
do
{
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Config")
let predicate = NSPredicate(format: "key == %#", "access_token")
fetchRequest.predicate = predicate
let fetchResults = try moc.fetch(fetchRequest) as? [Config]
if(fetchResults?.count > 0)
{
//NSLog((fetchResults?.first!.value)!)
return fetchResults?.first!.value
}
} catch let error as NSError{
NSLog(error.localizedDescription)
}
What is wrong with this piece of code?
EDIT: I can see the following code where persistentStoreCoordinator is set for managedObjectContext
lazy var managedObjectContext: NSManagedObjectContext = {
// Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.) This property is optional since there are legitimate error conditions that could cause the creation of the context to fail.
let coordinator = self.persistentStoreCoordinator
var managedObjectContext = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
managedObjectContext.persistentStoreCoordinator = coordinator
return managedObjectContext
}()