- Field( DCNS('subject.period'), 'epochs', salias='epoch', multiple=True),
- Field( DCNS('subject.type'), 'kinds', salias='kind', multiple=True),
- Field( DCNS('subject.genre'), 'genres', salias='genre', multiple=True),
+ Field( DCNS('subject.period'), 'epochs', salias='epoch', multiple=True,
+ required=False),
+ Field( DCNS('subject.type'), 'kinds', salias='kind', multiple=True,
+ required=False),
+ Field( DCNS('subject.genre'), 'genres', salias='genre', multiple=True,
+ required=False),