POST HOOK sometimes returns null branch (BB-11525)

Here's s sample post HOOK Payload, sometimes the value for branch is null and branches empty array even though we specify what branch to push on:
{
"repository": {
"website": "",
"fork": false,
"name": "mobi-puppet",
"scm": "git",
"owner": "mobitv",
"absolute_url": "/mobitv/mobi-puppet/",
"slug": "mobi-puppet",
"is_private": true
},
"truncated": false,
"commits": [
{
"node": "f77755153853",
"files": [
{
"type": "modified",
"file": "hiera-data/parameters/module/mobi_sprint_billing_adapter.yaml"
}
],
"branches": [],
"raw_author": "Sophia Xu [sxu%40mobitv.com]",
"utctimestamp": "2014-10-28 17:34:30+00:00",
"author": "sophiaxu",
"timestamp": "2014-10-28 18:34:30",
"raw_node": "f77755153853cd9a1fb4dac27b160da4ccc39f05",
"parents": [
"f76b48da8c7f"
],
"branch": null,
"message": "update mobi-sprint-billing-adapter version\n",
"revision": null,
"size": -1
},
{
"node": "dea4d1c6b104",
"files": [
{
"type": "modified",
"file": "hiera-data/parameters/module/mobi_sprint_billing_adapter.yaml"
}
],
"branches": [],
"raw_author": "Sophia Xu [sxu%40mobitv.com]",
"utctimestamp": "2014-10-28 17:39:35+00:00",
"author": "sophiaxu",
"timestamp": "2014-10-28 18:39:35",
"raw_node": "dea4d1c6b10440fcb4d10f93409b062b8c768d08",
"parents": [
"f77755153853"
],
"branch": null,
"message": "Revert "update mobi-sprint-billing-adapter version"\n\nThis reverts commit f77755153853cd9a1fb4dac27b160da4ccc39f05.\n",
"revision": null,
"size": -1
},
{
"node": "da5727fad124",
"files": [
{
"type": "modified",
"file": "hiera-data/parameters/module/mobi_sprint_billing_adapter.yaml"
}
],
"raw_author": "Sophia Xu [sxu%40mobitv.com]",
"utctimestamp": "2014-10-28 18:01:23+00:00",
"author": "sophiaxu",
"timestamp": "2014-10-28 19:01:23",
"raw_node": "da5727fad124b468bef7d4202bebc8baca51658b",
"parents": [
"dea4d1c6b104"
],
"branch": "SSC_329",
"message": "update mobi_sprint_billing_adapter version\n",
"revision": null,
"size": -1
}
],
"canon_url": "https://bitbucket.org",
"user": "sophiaxu"
}