React-admin: ReferenceField doesn't allow undefined values

[s-nel]

Use case:
I have an optional reference field on my entity whose value is either undefined or an id of another entity

Expected:
admin-on-rest checks the value of the record with the given source prop, and if undefined displays nothing, otherwise a request for the referenced entity is sent and the reference child field is displayed

Actual:
admin-on-rest sends a GET_MANY request with parameter ids as ["undefined"]

[fzaninotto]

Did you set the allowEmpty prop on <ReferenceField>?

[s-nel]

Yes I have. It didn't make a difference, and I can tell by code inspection no checks are made for undefined values and no tests are written for that case

[djhi]

Confirmed, that's a bug

[0zguner]

@fzaninotto can we do the same thing with ReferenceArrayField ? I can send a pr if you are okay with this.