Make SetPredicate and subclasses JSON serializable with Pydantic

Author: Aniketsy

pyiceberg/expressions/__init__.py

@@ -701,7 +701,7 @@ def __new__(  # type: ignore  # pylint: disable=W0221
 
     def __invert__(self) -> NotIn[L]:
         """Transform the Expression into its negated version."""
-        return NotIn[L](self.term, self.literals)
+        return NotIn[L](self.term, self._literals)
 
     @property
     def as_bound(self) -> Type[BoundIn[L]]: