Penerapan asas proporsionalitas sebagai landasan pertukaran hak dan kewajiban para pihak dalam perjanjian waralaba: studi kasus perjanjian waralaba Bangi Kopitiam antara PT. Indo Bangi Kopitiam dan PT. Trimitra Oryza Sativa = Implementation of principle of proportionality as the foundation of rights and obligations distribution for parties in the franchise agreement: case study on franchise agreement of Bangi Kopitiam between PT. Indo Bangi Kopitiam and PT. Trimitra Oryza Sativa