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dataclass.py

@@ -54,6 +54,15 @@ class RequiredField(Field):
         self.required = True
 
 
+@dataclasses.dataclass
+class OptionalField(Field):
+    def __post_init__(self):
+        self.required = False
+        assert (
+            self.default is not None or self.default_factory is not None
+        ), "OptionalField must have default or default_factory"
+
+
 @dataclasses.dataclass
 class AbstractField(Field):
     def __post_init__(self):