If a borrower and a lender go to Beis Din with a loan document that stipulates interest, but the borrower claims he can at least collect the principle, how does Beis Din look at that?
Do they recognize the loan document, but invalidate the interest, or do they invalidate the entire loan document as illegitimate and uncollectible?
What if the borrower or the lender claim that the interest was written into the document for legal reasons, but in fact they did not intent to charge/collect it. Does that change the answer? Does it matter which one is making the claim?