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You can speak with your PO and see if they will retest you and believe your story. If not, you are going to have to fight this, if you are violated. You would then have to convince the Judge, that you did not willfully or substantially violate your probate and the failed test was a result of the muffin. You will likely need to present some type of evidence, that will prove the amount of seeds in the muffin, would result in a failed test.
I am not talking about the muffin. You will need to do research and be able to show your PO and/or the Judge, that if you eat a muffin with poppy seeds, that it will result in the presence of opiates. There needs to be actual proof of this, not something that a friend told you or you saw on tv.