Decrypt AAAAAAAAAAAA with vigenere

Maybe someone can help me.
I have to decrypt the Vigenere Chiffre : AAAAAAAAAAAA
This is all what is given. So I have no keylength or something. I think I'm not supposed to do a brute force attack.
I actually do know how the decryption with Vigenere works. I have already written a program for a different text to translate. But my program works for texts consisting of a natural language. I did a frequency analysis of letters, bigrams.. But I don't know I can solve this problem here when there is only one letter 12 times.
Maybe this has something to do with redundancy and unicity length?
It may have to do something with redundancy and unicity length because this was part of my lecture the last time, but i don't know what to do with this information.
Thank you for your help

Given that your cyphertext is all As, I am going to assume that the key is of the same length as the plaintext (there are edge cases where this is technically untrue, but for decryption purposes it's probably true).
When your Vigenère key is as long as your plaintext, you are effectively using a Onetime pad, which is impossible to decrypt.