Mpesa constructor

Mpesa(int amount, String phoneNumber, { String? accountReference, String? transactionDesc, })

if account reference || transactionDesc is not defined its replaced with the phone number

Implementation

Mpesa(this.amount, this.phoneNumber,
    {this.accountReference, this.transactionDesc}) {
  accountReference ??= phoneNumber;
  transactionDesc ??= phoneNumber;
}