diff --git a/abacus_factory.yml b/abacus_factory.yml
deleted file mode 100644
index 13198227..00000000
--- a/abacus_factory.yml
+++ /dev/null
@@ -1,398 +0,0 @@
-- macro: OppDefaults
-  fields:
-    amount: 4
-    StageName: Prospecting
-    CloseDate: 2019-11-26
-    npe01__Do_Not_Automatically_Create_Payment__c: True
-
-- macro: npePaymentDefaults
-  fields:
-    npe01__Payment_Amount__c: 3
-    npe01__Paid__c: True
-    npe01__Payment_Method__c: Cheque
-    npe01__Check_Reference_Number__c: 12345
-    npe01__Payment_Date__c: 2019-11-26
-- macro: npeScheduledPaymentDefaults
-  fields:
-    npe01__Payment_Amount__c: 3
-    npe01__Payment_Method__c: Cheque
-    npe01__Check_Reference_Number__c: 12345
-    npe01__Scheduled_Date__c: 2019-12-26
-
-- object: npsp__General_Accounting_Unit__c
-  nickname: GAU1
-  just_once: True
-  fields:
-    name: GAU 1
-- object: npsp__General_Accounting_Unit__c
-  nickname: GAU2
-  just_once: True
-  fields:
-    name: GAU 2
-# - object: General_Accounting_Unit__c
-#   nickname: GAU3
-#   fields:
-#     name: GAU 3
-- object: npsp__General_Accounting_Unit__c
-  nickname: Default GAU
-  just_once: True
-  fields:
-    name: Default GAU
-
-- object: Account
-  nickname: Account1
-  fields:
-    name: Account 1
-- object: Account
-  nickname: Account2
-  fields:
-    name: Account 2
-- object: Account
-  nickname: Account3
-  fields:
-    name: Account 3
-- object: Account
-  nickname: Account4
-  fields:
-    name: Account 4
-- object: Account
-  nickname: Account5
-  fields:
-    name: Account 5
-- object: Account
-  nickname: Account6
-  fields:
-    name: Account 6
-
-- object: __Repeatable Grouper
-  count: 3
-  friends:
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_1
-      fields:
-        name: ABA-1.1a Soft Act. Open Oppty. Insert Partially Paid Pmt. Default GAU. GroupByAlloc
-        Revenue_Grouping_Scheme__c: 1
-        AccountId:
-          reference: Account1
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_2
-      fields:
-        name: ABA-1.1b Soft Act. Open Oppty. Insert Partially Paid Pmt. Default GAU. GroupByDate
-        Revenue_Grouping_Scheme__c: 2
-        AccountId:
-          reference: Account2
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_3
-      fields:
-        name: ABA-1.2a Soft Act. Open Oppty. Insert Partially Paid Pmt. 50% GAU1. GroupByAlloc
-        Revenue_Grouping_Scheme__c: 1
-        AccountId:
-          reference: Account3
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_4
-      fields:
-        name: ABA-1.2b Soft Act. Open Oppty. Insert Partially Paid Pmt. 50% GAU1. GroupByDate
-        Revenue_Grouping_Scheme__c: 2
-        AccountId:
-          reference: Account4
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_5
-      fields:
-        name: ABA-1.3a Soft Act. Open Oppty. 1 Paid Pmt 1 Sched Pmt. $50 GAU1. GroupByAlloc
-        Revenue_Grouping_Scheme__c: 1
-        AccountId:
-          reference: Account5
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_6
-      fields:
-        name: ABA-1.3b Soft Act. Open Oppty. 1 Paid Pmt 1 Sched Pmt. $50 GAU1. GroupByDate
-        Revenue_Grouping_Scheme__c: 2
-        AccountId:
-          reference: Account6
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_7
-      fields:
-        name: ABA-1.4a Soft Act. Open Oppty. 1 Written-Off Pmt. Default GAU. GroupByAlloc
-        Revenue_Grouping_Scheme__c: 1
-        AccountId:
-          reference: Account1
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_8
-      fields:
-        name: ABA-1.5a Soft Act. Open Oppty. 1 Paid Pmt 1 Refund. Default GAU. GroupByAlloc
-        Revenue_Grouping_Scheme__c: 1
-        AccountId:
-          reference: Account2
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_9
-      fields:
-        name: ABA-2.1a Hard Act. Pledged Oppty. Insert Sched Pmt. Default GAU. GroupByAlloc
-        StageName: Pledged
-        Revenue_Grouping_Scheme__c: 1
-        AccountId:
-          reference: Account3
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_10
-      fields:
-        name: ABA-2.1b Hard Act. Pledged Oppty. Insert Sched Pmt. Default GAU. GroupByDate
-        StageName: Pledged
-        Revenue_Grouping_Scheme__c: 2
-        AccountId:
-          reference: Account4
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_11
-      fields:
-        name: ABA-2.2a Hard Act. Closed Won Oppty. Insert Sched Pmt. Default GAU. GroupByAlloc
-        StageName: Closed Won
-        Revenue_Grouping_Scheme__c: 1
-        AccountId:
-          reference: Account5
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_12
-      fields:
-        name: ABA-2.3a Hard Act. Pledged Oppty. 2 Sched Pmts. 50% GAU1 40% GAU2. GroupByAlloc
-        StageName: Pledged
-        Revenue_Grouping_Scheme__c: 1
-        AccountId:
-          reference: Account6
-    - object: Opportunity
-      include: OppDefaults
-      nickname: Opportunity_13
-      fields:
-        name: ABA-2.3b Hard Act. Pledged Oppty. 2 Sched Pmts. 50% GAU1 40% GAU2. GroupByDate
-        StageName: Pledged
-        Revenue_Grouping_Scheme__c: 2
-        AccountId:
-          reference: Account1
-
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_1
-        npsp__General_Accounting_Unit__c:
-          reference: Default GAU
-        npsp__Amount__c: 100
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_2
-        npsp__General_Accounting_Unit__c:
-          reference: Default GAU
-        npsp__Amount__c: 100
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_3
-        npsp__General_Accounting_Unit__c:
-          reference: GAU1
-        npsp__Percent__c: 50
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_4
-        npsp__General_Accounting_Unit__c:
-          reference: GAU1
-        npsp__Percent__c: 50
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_5
-        npsp__General_Accounting_Unit__c:
-          reference: GAU1
-        npsp__Amount__c: 50
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_6
-        npsp__General_Accounting_Unit__c:
-          reference: GAU1
-        npsp__Amount__c: 50
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_7
-        npsp__General_Accounting_Unit__c:
-          reference: Default GAU
-        npsp__Amount__c: 100
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_8
-        npsp__General_Accounting_Unit__c:
-          reference: Default GAU
-        npsp__Amount__c: 100
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_9
-        npsp__General_Accounting_Unit__c:
-          reference: Default GAU
-        npsp__Amount__c: 100
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_10
-        npsp__General_Accounting_Unit__c:
-          reference: Default GAU
-        npsp__Amount__c: 100
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_11
-        npsp__General_Accounting_Unit__c:
-          reference: Default GAU
-        npsp__Amount__c: 100
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_12
-        npsp__General_Accounting_Unit__c:
-          reference: GAU1
-        npsp__Percent__c: 50
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_12
-        npsp__General_Accounting_Unit__c:
-          reference: GAU2
-        npsp__Percent__c: 40
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_13
-        npsp__General_Accounting_Unit__c:
-          reference: GAU1
-        npsp__Percent__c: 50
-    - object: npsp__Allocation__c
-      fields:
-        npsp__Opportunity__c:
-          reference: Opportunity_13
-        npsp__General_Accounting_Unit__c:
-          reference: GAU2
-        npsp__Percent__c: 40
-
-    - object: npe01__OppPayment__c
-      include: npePaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_1
-    - object: npe01__OppPayment__c
-      include: npePaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_2
-    - object: npe01__OppPayment__c
-      include: npePaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_3
-    - object: npe01__OppPayment__c
-      include: npePaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_4
-    - object: npe01__OppPayment__c
-      include: npePaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_5
-        npe01__Payment_Amount__c: 50
-    - object: npe01__OppPayment__c
-      include: npeScheduledPaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_5
-        npe01__Payment_Amount__c: 25
-    - object: npe01__OppPayment__c
-      include: npePaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_6
-        npe01__Payment_Amount__c: 50
-    - object: npe01__OppPayment__c
-      include: npeScheduledPaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_6
-        npe01__Payment_Amount__c: 25
-    - object: npe01__OppPayment__c
-      include: npePaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_7
-        npe01__Payment_Amount__c: 50
-        npe01__Paid__c: False
-        npe01__Written_Off__c: True
-    - object: npe01__OppPayment__c
-      include: npePaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_8
-        npe01__Payment_Amount__c: 50
-    - object: npe01__OppPayment__c
-      include: npePaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_8
-        npe01__Payment_Amount__c: -25
-    - object: npe01__OppPayment__c
-      include: npeScheduledPaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_9
-        npe01__Payment_Amount__c: 100
-        npe01__Payment_Method__c: Cash
-    - object: npe01__OppPayment__c
-      include: npeScheduledPaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_10
-        npe01__Payment_Amount__c: 100
-        npe01__Payment_Method__c: Cash
-    - object: npe01__OppPayment__c
-      include: npeScheduledPaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_11
-        npe01__Payment_Amount__c: 100
-        npe01__Payment_Method__c: Cash
-    - object: npe01__OppPayment__c
-      include: npeScheduledPaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_12
-        npe01__Payment_Amount__c: 25
-        npe01__Payment_Method__c: Cash
-    - object: npe01__OppPayment__c
-      include: npeScheduledPaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_12
-        npe01__Payment_Amount__c: 75
-        npe01__Payment_Method__c: Cash
-    - object: npe01__OppPayment__c
-      include: npeScheduledPaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_13
-        npe01__Payment_Amount__c: 25
-        npe01__Payment_Method__c: Cash
-    - object: npe01__OppPayment__c
-      include: npeScheduledPaymentDefaults
-      fields:
-        npe01__Opportunity__c:
-          reference: Opportunity_13
-        npe01__Payment_Amount__c: 75
-        npe01__Payment_Method__c: Cash
diff --git a/snowfakery/data_generator_runtime_dom.py b/snowfakery/data_generator_runtime_dom.py
index 10198488..0db3aae4 100644
--- a/snowfakery/data_generator_runtime_dom.py
+++ b/snowfakery/data_generator_runtime_dom.py
@@ -18,7 +18,7 @@
 
 # objects that represent the hierarchy of a data generator.
 # roughly similar to the YAML structure but with domain-specific objects
-Scalar = Union[str, Number, date, datetime]
+Scalar = Union[str, Number, date, datetime, None]
 FieldValue = Union[None, Scalar, ObjectRow, tuple]
 Definition = Union["ObjectTemplate", "SimpleValue", "StructuredValue"]
 
diff --git a/snowfakery/parse_factory_yaml.py b/snowfakery/parse_factory_yaml.py
index 2bcd52e8..adae1ac8 100644
--- a/snowfakery/parse_factory_yaml.py
+++ b/snowfakery/parse_factory_yaml.py
@@ -53,7 +53,13 @@ def __init__(self, name):
         self._templates = []
 
     def register(self, template: ObjectTemplate) -> None:
-        self.fields.update({field.name: field for field in template.fields})
+        self.fields.update(
+            {
+                field.name: field
+                for field in template.fields
+                if not field.name.startswith("__")
+            }
+        )
         self.friends.update({friend.tablename: friend for friend in template.friends})
         self._templates.append(template)
 
@@ -175,11 +181,7 @@ def parse_structured_value(
 def parse_field_value(
     name: str, field, context: ParseContext, allow_structured_values=True
 ) -> Union[SimpleValue, StructuredValue, ObjectTemplate]:
-    if field is None:
-        raise DataGenSyntaxError(
-            f"Field should not be empty: {name}", **context.line_num(field)
-        )
-    if isinstance(field, (str, Number, date)):
+    if isinstance(field, (str, Number, date, type(None))):
         return SimpleValue(field, **(context.line_num(field) or context.line_num()))
     elif isinstance(field, dict) and field.get("object"):
         with context.change_current_parent_object(field):
@@ -199,10 +201,6 @@ def parse_field_value(
 
 def parse_field(name: str, definition, context: ParseContext) -> FieldFactory:
     assert name, name
-    if definition is None:
-        raise DataGenSyntaxError(
-            f"Field should have a definition: {name}", **context.line_num(name)
-        )
     return FieldFactory(
         name,
         parse_field_value(name, definition, context),
diff --git a/snowfakery/utils/template_utils.py b/snowfakery/utils/template_utils.py
index 6206b6f0..1f19474d 100644
--- a/snowfakery/utils/template_utils.py
+++ b/snowfakery/utils/template_utils.py
@@ -27,7 +27,7 @@ def __init__(self, func):
         self.func = func
 
     def __str__(self):
-        return self.func()
+        return str(self.func())
 
     def __call__(self, *args, **kwargs):
         return self.func(*args, **kwargs)
diff --git a/tests/test_errors.py b/tests/test_errors.py
index efdad509..4a224c97 100644
--- a/tests/test_errors.py
+++ b/tests/test_errors.py
@@ -76,19 +76,6 @@ def test_extra_keys(self):
             generate(StringIO(yaml))
         assert 4 > e.exception.line_num >= 2
 
-    def test_missing_field_value(self):
-        yaml = """
-            - object: Person
-              count: 5
-              fields:
-                gender: Male
-                name:
-        """
-        with self.assertRaises(DataGenError) as e:
-            generate(StringIO(yaml))
-        assert "name" in str(e.exception)
-        assert "Field" in str(e.exception)
-
     def test_missing_param(self):
         yaml = """
             - object: Person
@@ -100,4 +87,4 @@ def test_missing_param(self):
         """
         with self.assertRaises(DataGenError) as e:
             generate(StringIO(yaml))
-        assert "Field" in str(e.exception)
+        assert "Problem rendering field" in str(e.exception)
diff --git a/tests/test_output_streams.py b/tests/test_output_streams.py
index 0aa1ffb1..44df422c 100644
--- a/tests/test_output_streams.py
+++ b/tests/test_output_streams.py
@@ -64,6 +64,16 @@ def test_bool(self):
         values = self.do_output(yaml)["foo"][0]
         assert str(values["is_true"]) == "1"
 
+    def test_null(self):
+        yaml = """
+        - object: foo
+          fields:
+            is_null:
+            """
+        values = self.do_output(yaml)["foo"][0]
+        print(values)
+        assert values["is_null"] is None
+
     def test_flushes(self):
         yaml = """
         - object: foo
@@ -139,9 +149,19 @@ def do_output(self, yaml):
                 }
                 return tables
 
+    def test_null(self):
+        yaml = """
+        - object: foo
+          fields:
+            is_null:
+            """
+        values = self.do_output(yaml)["foo"][0]
+        assert values["is_null"] is None
+
 
 class JSONTables:
     def __init__(self, json_data, table_names):
+        self.raw = json_data
         self.data = json.loads(json_data)
         self.tables = {table_name: [] for table_name in table_names}
         for row in self.data:
@@ -196,9 +216,28 @@ def test_from_cli(self):
         x = StringIO()
         with redirect_stdout(x):
             generate_cli.callback(
-                yaml_file=sample_yaml, output_format="json", output_files=["-"]
+                yaml_file=sample_yaml, output_format="json",
             )
-        # TODO: more validation!
+        data = json.loads(x.getvalue())
+        assert data == [
+            {
+                "_table": "Account",
+                "id": 1,
+                "name": "Default Company Name",
+                "ShippingCountry": "Canada",
+            }
+        ]
+
+    def test_null(self):
+        yaml = """
+        - object: foo
+          fields:
+            is_null:
+            """
+        output = self.do_output(yaml)
+        assert "null" in output.raw
+        values = output["foo"][0]
+        assert values["is_null"] is None
 
 
 class TestCSVOutputStream(unittest.TestCase, OutputCommonTests):
@@ -245,3 +284,15 @@ def test_csv_output(self):
                     "foo.csv",
                     "bar.csv",
                 }
+
+    def test_null(self):
+        yaml = """
+        - object: foo
+          fields:
+            is_null:
+            """
+        values = self.do_output(yaml)["foo"][0]
+        print(values)
+        assert (
+            values["is_null"] == ""
+        )  # CSV is no way of distingushing null from empty str