Ignore the write with `proposedValue === undefined`

[bmblb]

Feels wrong to merge null and undefined values. undefined is smth that doesn't exist, null on the other hand is smth that exists, but doesn't have value.
This makes write(identifier, undefined) same as write(identifier, null). Latter is definitely user wanting to null the value. First doesn't make sense to call deliberately, rather a handy filter for undefined values - if undefined is passed then do nothing.

chronograph/src/chrono/Transaction.ts

Line 455 in 0db8d13

if (proposedValue === undefined) proposedValue = null

[bmblb]

Another implication: default values are ignored. Scheduling engine passes quite a few undefined values to engine, hoping that default value will be taken. Like lag. But it doesn't happen.

[canonic-epicure]

Currently by design, for the scenario:

const someObject = {}
// lets say at this point `entity.someField` === 10
entity.someField = someObject.someField // undefiend

entity.someField === ??

User expectation is probably that entity.someField is "nullyfied" somehow, either to undefined or null (since graph does not contain undefined)

Need more feedback to proceed with such change.