setting counter column default instantiation value to 0 (not None)

cqlengine/columns.py

@@ -246,9 +246,18 @@ class Integer(Column):
         return self.validate(value)
 
 
+class CounterValueManager(BaseValueManager):
+    def __init__(self, instance, column, value):
+        super(CounterValueManager, self).__init__(instance, column, value)
+        self.value = self.value or 0
+        self.previous_value = self.previous_value or 0
+
+
 class Counter(Integer):
     db_type = 'counter'
 
+    value_manager = CounterValueManager
+
     def __init__(self,
                  index=False,
                  db_field=None,

cqlengine/tests/columns/test_counter_column.py

@@ -59,6 +59,15 @@ class TestCounterColumn(BaseCassEngTestCase):
 
     def test_update_from_none(self):
         """ Tests that updating from None uses a create statement """
+        instance = TestCounterModel()
+        instance.counter += 1
+        instance.save()
+
+        new = TestCounterModel.get(partition=instance.partition)
+        assert new.counter == 1
+
+    def test_new_instance_defaults_to_zero(self):
+        """ Tests that instantiating a new model instance will set the counter column to zero """
+        instance = TestCounterModel()
+        assert instance.counter == 0
 
-    def test_multiple_inserts(self):
-        """ Tests inserting over existing data works as expected """