Exception accessing a numpy inside a persistent StorageObj

[yolandab]

Accessing an numpy attribute inside a persistent StorageObj fails. The following code throws an exception

class myclass(StorageObj);
 '''
@ClassField myattr numpy.ndarray
'''
o=myclass("name")
x=np.ones(4)
o.myattr=x
print(o.myattr)

The message of the exception is:
TypeError: unsupported operand type(s) for //: 'int' and 'NoneType'