Partial update of existing documents. If a document does not exist, no update will be performed and it gets the result status 'NOT_FOUND'. In case a document is a master product with variants, the provided master product may only contain the changed values. However if some of the variants should be updated, all data from all variant products are required, unless you have an ID data-field inside variant - then you can update single variants. Without variant ID field, the missing variants won't be there after the update! This is how single variants can be deleted.