In 6.2.1, Attribute Null of [CSDL] , specify the following: If the edm:Property element contains a Type attribute that specifies a collection, the property MUST always exist, but the collection MAY be empty. In this case, the Nullable attribute applies to members of the collection and specifies whether the collection can contain null values. Accepted: https://www.oasis-open.org/committees/download.php/50924/odata-meeting-55_on-20131003-minutes.html#odata-543