SWIS update to reset unmanagefrom/unmanageuntil field to NULL in the interface database table

I got the interface Uri by a Python SWIS REST request and now want to unmanage and remanage some interfaces. Question is how do I reset the value of unmanagefrom/unmanageuntil field back to NULL in the database table?

if I do 'swis.update(uri, unmanaged=False, unmanagefrom=0, unmanageuntil=0)' to remanage an interface, the value gets reset to 1/1/1900 whereas it should be reset to NULL.

if I do 'swis.update(uri, unmanaged=False, unmanagefrom=None, unmanageuntil=None)', it simply doesn't do anything.

Thanks in advance

Daniel