Remove None for dict.get()

Because If no default value is specified it defaults to None already.

Change-Id: I2b2ad6d80b4f36bf01b8f4c6ecfb6bbd6d62e75b

ceilometer/nova_client.py

@@ -102,7 +102,7 @@ class Client(object):
         image_metadata = getattr(image, 'metadata', None)
 
         for attr in ['kernel_id', 'ramdisk_id']:
-            ameta = image_metadata.get(attr, None) if image_metadata else None
+            ameta = image_metadata.get(attr) if image_metadata else None
             setattr(instance, attr, ameta)
 
     @logged