Removed Type, used Optional

tests/fixtures_domain2.py

-from typing import List, TypeVar
+from typing import List, Optional
 from domain2 import DomainObject, annotate
 
 
@@ -22,7 +22,7 @@ class DomainEntryB(DomainObject):
 
 class DomainEntryC(DomainObject):
     """B class"""
-    ref: '_FieldDomainEntryA'
+    ref: Optional['_FieldDomainEntryA']
     refs: List['_FieldDomainEntryB'] = []
 
 

tests/test_domain2.py

@@ -63,3 +63,15 @@ def test_int_ref_chain():
         DomainEntryB.model_construct(id=2, refs=[12, 13])
     ]
     assert container2.ref == DomainEntryA.model_construct(id=3, name='Name 3')
+
+def test_ref_optional():
+    container = DomainEntryC.model_construct(id=4, ref=None, refs=[1, 2])
+    container2 = DomainEntryC.model_validate(container, strict=True)
+    assert container.ref is None
+    assert container2.ref is None
+
+
+def test_ref_optional_2():
+    container = DomainEntryC.model_construct(id=4, refs=[1, 2])
+    with pytest.raises(ValidationError, match="1 validation error for DomainEntryC"):
+        DomainEntryC.model_validate(container, strict=True)
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