I've had an issue in my code and created transaction with fee object having fee equal to NaN. Your endpoint trans/add accepted this as valid value. However response was invalid JSON and trans/show has invalid json response
transaction $oid: 55dc833886c2734bf66f67dc
For this transaction, it seems like you had supplied the fees as 237.60 USD not Nan.
Having said that, Nan, None or 0 are acceptable values as well, which means that your facilitator fee is $0.00.