<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def eval(self, packet):
 """Returns the result of evaluating this DNToEUConversion in the context of the given Packet. """

        result = None
        terms  = None

        if self._when is None or self._when.eval(packet):
            result = self._equation.eval(packet)

        return result