Bava Metzia 94 - Conditions in Contracts
We saw that an unpaid custodian, who is just doing his fellow a favor, may be obligated to take an oath that he was caring well for the article.
To prevent this, before he undertakes the care, he may stipulate to be exempt from an oath. In the same way, a borrower may stipulate to be exempt from paying.
However, he seems to be stipulating against the Torah rule! - No, he is just saying that he does not want to become an unpaid custodian at all,
but rather he is only accepting a separate agreement, which limits his liability.
In general, whoever makes a stipulation contrary to what is written in the Torah, his stipulation is void. Any stipulation after the action is void. For example, "This item is yours on condition that you walk a mile" - the items is his and he does not have to walk. Any stipulation that is impossible to fulfill is void. For example, "This is your Get on condition that you cross the sea on foot" - the condition is void, the Get is valid, and the woman is divorced.
There is also a special leniency for borrowers: if one borrows a cow but hires the owner along with it, he is not liable if the cow dies.
Art: Woman in White on a Beach by Peder Severin Kroyer