Error in assert

There is an error in initial code: assert encode("attack at 12:00 am", "na1c3h8tb2ome5wrpd4f6g7i9j0kjqsuvxyz", "privacy") == 'DGDDDAGDDGAFADDFDADVDVFAADVX', "encode attack"

The string 'na1c3h8tb2ome5wrpd4f6g7i9j0kjqsuvxyz' has duplicates ('j'). But according to Precondition: len(set(secretalphabet)) == len(secretalphabet)

From: https://py.checkio.org/mission/adfgvx-cipher/solve/

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