class MyRecord(Record): id = nullable(val_type)
class MyRecord(Record): children = nullable(pair_of(RecursiveType))
class MyRecord(Record): nxt = nullable(RecursiveType)
class MyRecord(Record): v = nullable(dict_of(int, int))
class MyRecord(Record): x = int y = nullable(int)
class MyRecord(Record): v = nullable(set_of(int))
class MyRecord(Record): v = nullable(pair_of(int))
class MyRecord(Record): s = nullable(uppercase_wchars(10))
class MyRecord(Record): v = nullable(one_of('a', 'b', 'c'))
class MyRecord(Record): value = nullable(object, default=obj)