A mutation to update an existing Item.
When updating Items, bear in mind that an Item can only have actual date(s) (a single date or Start and End Dates) or a bucket time, but not both.
If the intent is to update an existing standalone Item to convert it to a sub-Item or to change the family in which an existing sub-Item belongs, a valid parentItemID must be specified. All in-app restrictions pertaining to sub-items will also be enforced via the API (eg. maximum number of allowed sub-Items in a given family).
If the intent is to update an existing sub-Item to a standalone Item, ensure that the parentItemID is NULL.
Note that the updateItem call will only modify fields which are explicitly specified in the call’s arguments. Fields not specified in the arguments in the API call will retain their existing values.