<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def _validate_value(self, proposal):
        "Replace all values with the actual objects in the options list"
        try:
            return tuple(findvalue(self._options_values, i, self.equals) for i in proposal.value)
        except ValueError:
            raise TraitError('Invalid selection: value not found')