PynamoDB model.update_item bug in LBA

run.py

from pynamodb.models import Model
from pynamodb.attributes import (
    UnicodeAttribute, LegacyBooleanAttribute, BooleanAttribute)


class UserModel(Model):
    class Meta:
        host = "http://localhost:8000"
        table_name = "UserModel2"
    id = UnicodeAttribute(hash_key=True)
    foo = BooleanAttribute()
    bar = UnicodeAttribute(null=True)

class UserModel2(Model):
    class Meta:
        host = "http://localhost:8000"
        table_name = "UserModel2"
    id = UnicodeAttribute(hash_key=True)
    foo = LegacyBooleanAttribute()
    bar = UnicodeAttribute(null=True)

if UserModel.exists():
    UserModel.delete_table()

UserModel.create_table(read_capacity_units=2, write_capacity_units=2)


u1 = UserModel(id="item1", foo=True, bar="item1")
u1.save()

u1 = UserModel2.get('item1')
#json error TypeError: expected string or buffer (value written by BA isn't readable by LBA)
u1.update_item('bar', "item1_update", 'PUT')