only values starting with int possible -> only positive values

InvenTree/InvenTree/serializers.py

@@ -248,8 +248,6 @@ class ReferenceIndexingSerializerMixin():
     for the BigIntegerField
     """
     def validate_reference(self, value):
-        if extract_int(value) < -models.BigIntegerField.MAX_BIGINT:
-            raise serializers.ValidationError('reference is to to small')
         if extract_int(value) > models.BigIntegerField.MAX_BIGINT:
             raise serializers.ValidationError('reference is to to big')
         return value

InvenTree/order/test_api.py

@@ -124,16 +124,6 @@ class PurchaseOrderTest(OrderTest):
             expected_code=400
         )
 
-        # too small
-        self.post(
-            url,
-            {
-                'supplier': 1,
-                'reference': -huge_numer,
-                'description': 'PO not created via the API',
-            },
-            expected_code=400
-        )
 
     def test_po_attachments(self):