You might have an argument if there was no authentication/error-detection on the ciphertext, such that many keys would give valid decodings, and more so if it was a simple xor, such that any plain text could be a valid decoding given the appropriate key. But that's not a remotely practical cryptosystem for several reasons.

This seems like a highly questionable metaphysical argument. The decryption key does exist and, therefore, so does the information. The question is just who has access to that passcode.

I can't see a judge swallowing that logic, you do have something similar to a metal safe's key and you've refused to provide it