When I started working with version 10, I noticed that fields when having no value used to return nothing (“NULL”/“No Value”). But later on when working with v11, I came to know it is returning undefined. But recently, I noticed that some fields again are returning NULL rather than undefined . I tested with some fields and found the pattern that when we had to enter some values to a field (Data,Small Text) if those fields are null, it is still returning undefined. But fields where we had to select value (Select, Link) they are now returning " " (empty/nothing) but I remember very well they also used to return undefined on no value.
Can anyone throw some light on the statement of mine. I’m kindof confused for now. 
Thanks In Advance.