Rails raises an exception for missing translation variable at validation

Question

I have this translation:

contract: "I agree with terms and conditions of the <a href='%{contract_link}' target='_blank'>funding agreement</a> and the <a href='%{mandate_link}' target='_blank'>lawyer's mandate</a>"

When calling user.valid? , it raises missing interpolation argument :contract_link exception even though I've defined a message error in my model.

validates_acceptance_of :contract,
  on: :create,
  allow_nil: false,
  message: :contract_not_accepted,
  if: :user_has_to_accept_contract?

If I temporarily remove the variable, everything works fine.

Any idea how I can fix this behavior?