invoiceNumber is not needed in CreditJson, and it is not set correctly when not supplied in POST

[sbrossie]

http://10.18.56.145:8080/1.0/kb/accounts/bc018d37-b758-45fb-9135-b1996d43bcc8/timeline
...
"invoices": [
{
"accountId": "bc018d37-b758-45fb-9135-b1996d43bcc8",
"amount": 0,
"balance": 0.0,
"bundleKeys": "2025736",
"cba": 0.0,
"creditAdj": 0.0,
"credits": [
{
"accountId": "bc018d37-b758-45fb-9135-b1996d43bcc8",
"creditAmount": -0.01,
"effectiveDate": "2012-08-09T00:00:00.000-08:00",
"invoiceId": "e8242530-8fee-420a-8fb4-ab8bfe8961e0",
"invoiceNumber": null,
"reason": null,
"requestedDate": null
}
],
"invoiceDate": "2012-07-16",
"invoiceId": "42f52d03-d2da-4912-bd2f-81695bb97627",
"invoiceNumber": "1",
"refundAdj": 0.0,
"targetDate": "2012-07-16"
},
...