bdm: store empty object as connection_info by default

There are several code paths which expect connection_info to be
a valid JSON object.  However, if we don't find a value, we are
setting it to an initial value of 'None' which evenutally gets
converted to 'null' as JSON and stored in the database.

This patch sets the default value to {} so that any new block
device mappings have an empty object, rather than NULL.

Closes-Bug: #1821244
Change-Id: I15a7c13edf78884ec223fd531a78a341106b41b8

Author: mnaser

nova/tests/unit/virt/test_block_device.py

@@ -120,6 +120,31 @@ class TestDriverBlockDevice(test.NoDBTestCase):
         'connection_info': {"fake": "connection_info"},
         'delete_on_termination': False}
 
+    volume_bdm_dict_without_conn_info = block_device.BlockDeviceDict(
+        {'id': 3, 'instance_uuid': uuids.instance,
+         'device_name': '/dev/sda1',
+         'source_type': 'volume',
+         'disk_bus': 'scsi',
+         'device_type': 'disk',
+         'volume_size': 8,
+         'destination_type': 'volume',
+         'volume_id': 'fake-volume-id-1',
+         'guest_format': 'ext4',
+         'connection_info': None,
+         'delete_on_termination': False,
+         'boot_index': 0})
+
+    volume_driver_bdm_without_conn_info = {
+        'attachment_id': None,
+        'mount_device': '/dev/sda1',
+        'connection_info': {},
+        'delete_on_termination': False,
+        'disk_bus': 'scsi',
+        'device_type': 'disk',
+        'guest_format': 'ext4',
+        'boot_index': 0,
+        'volume_type': None}
+
     volsnapshot_bdm_dict = block_device.BlockDeviceDict(
         {'id': 4, 'instance_uuid': uuids.instance,
          'device_name': '/dev/sda2',
@@ -223,6 +248,8 @@ def setUp(self):
             self.context, self.ephemeral_bdm_dict)
         self.volume_bdm = fake_block_device.fake_bdm_object(
             self.context, self.volume_bdm_dict)
+        self.volume_bdm_without_conn_info = fake_block_device.fake_bdm_object(
+            self.context, self.volume_bdm_dict_without_conn_info)
         self.volsnapshot_bdm = fake_block_device.fake_bdm_object(
             self.context, self.volsnapshot_bdm_dict)
         self.volimage_bdm = fake_block_device.fake_bdm_object(
@@ -1199,6 +1226,11 @@ def test_convert_volume(self):
                          driver_block_device.convert_volume(
                              self.volsnapshot_bdm))
 
+    def test_convert_volume_without_connection_info(self):
+        self.assertEqual(self.volume_driver_bdm_without_conn_info,
+                         driver_block_device.convert_volume(
+                             self.volume_bdm_without_conn_info))
+
     def test_legacy_block_devices(self):
         test_snapshot = self.driver_classes['volsnapshot'](
             self.volsnapshot_bdm)

nova/virt/block_device.py

@@ -281,11 +281,13 @@ def _transform(self):
              if k in self._new_fields | set(['delete_on_termination'])}
         )
         self['mount_device'] = self._bdm_obj.device_name
+        # connection_info might not be set so default to an empty dict so that
+        # it can be serialized to an empty JSON object.
         try:
             self['connection_info'] = jsonutils.loads(
                 self._bdm_obj.connection_info)
         except TypeError:
-            self['connection_info'] = None
+            self['connection_info'] = {}
         # volume_type might not be set on the internal bdm object so default
         # to None if not set
         self['volume_type'] = (