VM's CPU number.

src/MappedCollection.coffee

@@ -230,7 +230,7 @@ class $MappedCollection
                   hook.call ctx, value, key
 
                   # Updates the value if it changed.
-                  $setDeep item.value, path if ctx.field isnt field
+                  $setDeep item.value, path, ctx.field if ctx.field isnt field
 
             # Checks each hook is correctly defined.
             {enter, update, exit} = hooks_

src/spec.coffee

@@ -284,9 +284,12 @@ module.exports = (refsToUUIDs) ->
               update: (metrics, UUID) ->
                 return if UUID isnt refsToUUIDs[@generator.metrics]
 
-                @field = for _, utilisation of metrics.VCPUs_utilisation
+                i = 0
+                n = metrics.VCPUs_number
+                @field = while i++ < n
                   {
-                    usage: utilisation
+                    # TODO: Should it be null?
+                    usage: 0
                   }
             }
           }

src/xo.coffee

@@ -204,7 +204,6 @@ class $XO
       # Remembers its UUID.
       poolUUID = pool.uuid
 
-
       # Normalizes the records.
       normalizeObject pool, ref, 'pool'