HQL path expressions into @Struct aggregate embeddable fields are supported in HIBERNATE-93. Operations on a whole @Struct embeddable are not.

is [not] null on a whole @Struct field throws FeatureNotSupportedException.

Repro:

  from ItemWithNestedValue where nested is null
  from ItemWithNestedValue where nested is not null

Observed:

  FeatureNotSupportedException: Only the following nullness predicates are supported: field is [not] null

Cause: the nullness predicate handling in AbstractMqlTranslator does not handle a whole-aggregate target; Hibernate does not expand it to a bare ColumnReference.

Out of scope for HIBERNATE-93 (path expressions into structs).