TypeError in `issubclass` call in Index._init_ if component of composite key or index is redefined

[shintoo]

Malformed schema:

# test.py
class A(db.Entity):
    foo = Required(int)
    bar = Required(int)
    PrimaryKey(foo, bar) # Also true for composite_key and composite_index
    bar = Required(int)

Error:

Traceback (most recent call last):
  File "test.py", line 16, in <module>
    class A(db.Entity):
  File "<string>", line 2, in __init__
  File "pony/utils/utils.py", line 78, in cut_traceback
    reraise(exc_type, exc, full_tb)
  File "pony/utils/utils.py", line 95, in reraise
    try: raise exc.with_traceback(tb)
  File "pony/utils/utils.py", line 61, in cut_traceback
    try: return func(*args, **kwargs)
  File "pony/orm/core.py", line 3792, in __init__
    for index in indexes: index._init_(entity)
  File "pony/orm/core.py", line 2644, in _init_
    if not issubclass(entity, attr.entity): throw(ERDiagramError,
TypeError: issubclass() arg 2 must be a class or tuple of classes

Adding a print before that line:

core.py L2644:
	entity: <class 'test.A'>
        type(attr): <class `pony.orm.core.Required`>
	attr: ?.?
	attr.entity: None