How to use the environs.__init__.EnvSealedError function in environs

def method(
        self: "Env", name: str, default: typing.Any = ma.missing, subcast: typing.Type = None, **kwargs
    ):
        if self._sealed:
            raise EnvSealedError("Env has already been sealed. New values cannot be parsed.")
        parsed_key, raw_value, proxied_key = self._get_from_environ(name, default)
        if raw_value is ma.missing:
            raise EnvError('Environment variable "{}" not set'.format(proxied_key or parsed_key))
        value = func(raw_value, **kwargs)
        self._fields[parsed_key] = ma.fields.Field(**kwargs)
        self._values[parsed_key] = value
        return value

def method(
        self: "Env", name: str, default: typing.Any = ma.missing, subcast: Subcast = None, **kwargs
    ) -> _T:
        if self._sealed:
            raise EnvSealedError("Env has already been sealed. New values cannot be parsed.")
        missing = kwargs.pop("missing", None) or default
        if isinstance(field_or_factory, type) and issubclass(field_or_factory, ma.fields.Field):
            field = field_or_factory(missing=missing, **kwargs)
        else:
            field = field_or_factory(subcast=subcast, missing=missing, **kwargs)
        parsed_key, raw_value, proxied_key = self._get_from_environ(name, ma.missing)
        self._fields[parsed_key] = field
        source_key = proxied_key or parsed_key
        if raw_value is ma.missing and field.missing is ma.missing:
            message = "Environment variable not set."
            if self.eager:
                raise EnvValidationError('Environment variable "{}" not set'.format(source_key), [message])
            else:
                self._errors[parsed_key].append(message)
        if raw_value or raw_value == "":
            value = raw_value