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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def to_event(self, event_type, field_name=None, depth=None):
 """Constructs an IonEvent from this _IonNature value. Args: event_type (IonEventType):
 The type of the resulting event. field_name (Optional[text]):
 The field name associated with this value, if any. depth (Optional[int]):
 The depth of this value. Returns: An IonEvent with the properties from this value. """

        if self.ion_event is None:
            value = self
            if isinstance(self, IonPyNull):
                value = None
            self.ion_event = IonEvent(event_type, ion_type=self.ion_type, value=value, field_name=field_name,
                                      annotations=self.ion_annotations, depth=depth)
        return self.ion_event