diff --git a/ironic/api/controllers/v1/allocation.py b/ironic/api/controllers/v1/allocation.py
index af346dd208..ab157d698c 100644
--- a/ironic/api/controllers/v1/allocation.py
+++ b/ironic/api/controllers/v1/allocation.py
@@ -117,6 +117,12 @@ class Allocation(base.APIBase):
         if fields is not None:
             api_utils.check_for_invalid_fields(fields, allocation.fields)
 
+        # Make the default values consistent between POST and GET API
+        if allocation.candidate_nodes is None:
+            allocation.candidate_nodes = []
+        if allocation.traits is None:
+            allocation.traits = []
+
         allocation = cls._convert_with_links(allocation,
                                              pecan.request.host_url)
 
diff --git a/ironic/tests/unit/api/controllers/v1/test_allocation.py b/ironic/tests/unit/api/controllers/v1/test_allocation.py
index bcb3ccad66..0637903aef 100644
--- a/ironic/tests/unit/api/controllers/v1/test_allocation.py
+++ b/ironic/tests/unit/api/controllers/v1/test_allocation.py
@@ -403,11 +403,15 @@ class TestPost(test_api_base.BaseApiTest):
         self.assertEqual(adict['uuid'], response.json['uuid'])
         self.assertEqual('allocating', response.json['state'])
         self.assertIsNone(response.json['node_uuid'])
+        self.assertEqual([], response.json['candidate_nodes'])
+        self.assertEqual([], response.json['traits'])
         result = self.get_json('/allocations/%s' % adict['uuid'],
                                headers=self.headers)
         self.assertEqual(adict['uuid'], result['uuid'])
         self.assertFalse(result['updated_at'])
         self.assertIsNone(result['node_uuid'])
+        self.assertEqual([], result['candidate_nodes'])
+        self.assertEqual([], result['traits'])
         return_created_at = timeutils.parse_isotime(
             result['created_at']).replace(tzinfo=None)
         self.assertEqual(test_time, return_created_at)