v4.2.0

Behaviour changes

• admin: Lists, checkboxes and multiselects with multiple never hold null: a stored null loads as their default, or [], without making the data dirty. Multiselects with multiple default to [] like checkboxes, and their clear button sets [], so new and cleared multiselects are sent as [] instead of null. To store empty values as null, return it from serializeValue(). Objects and single choices keep null.
• admin: required rejects empty arrays, so required lists and fields with multiple values need at least one entry. The server's required still accepts them.

Fixes

• ui: Date and time pickers show their value again when the focus leaves text that isn't a valid date or time, instead of keeping the text.