When Signing a contract the check of the lines is this code in CU 5944:
FromServContractLine.Reset();
FromServContractLine.SetRange("Contract Type", FromServContractHeader."Contract Type");
FromServContractLine.SetRange("Contract No.", FromServContractHeader."Contract No.");
FromServContractLine.SetRange("Line Amount", 0);
FromServContractLine.SetFilter("Line Discount %", '