Add non negative constraint to span offset

backend/data_import/pipeline/label.py

@@ -2,7 +2,7 @@ import abc
 import uuid
 from typing import Any, Optional
 
-from pydantic import UUID4, BaseModel, validator
+from pydantic import UUID4, BaseModel, NonNegativeInt, validator
 
 from .label_types import LabelTypes
 from examples.models import Example
@@ -70,8 +70,8 @@ class CategoryLabel(Label):
 
 class SpanLabel(Label):
     label: str
-    start_offset: int
-    end_offset: int
+    start_offset: NonNegativeInt
+    end_offset: NonNegativeInt
 
     def __lt__(self, other):
         return self.start_offset < other.start_offset

backend/data_import/tests/test_label.py

@@ -82,6 +82,10 @@ class TestSpanLabel(TestLabel):
         self.assertEqual(span.start_offset, 0)
         self.assertEqual(span.end_offset, 1)
 
+    def test_invalid_negative_offset(self):
+        with self.assertRaises(ValueError):
+            SpanLabel(label="A", start_offset=-1, end_offset=1, example_uuid=uuid.uuid4())
+
     def test_parse_invalid_dict(self):
         example_uuid = uuid.uuid4()
         with self.assertRaises(ValueError):