private function getUnresolvedField(Field $field, string $locale = null)
    {
        // The field is not currently available on this resource,
        // but it exists in the content type, so we return an appropriate
        // default value.
        if (!isset($this->fields[$field->getId()])) {
            return 'Array' === $field->getType() ? [] : null;
        }

        $value = $this->fields[$field->getId()];

        // This also checks two things:
        // * the compatibility of the given locale with the one present in sys.locale
        // * the existence of the given locale among those available in the environment
        // If we're trying to access locale X and the entry was built with locale Y,
        // or the environment does not support such locale, an exception will be thrown.
        // To allow accessing multiple locales on a single entry, fetching it
        // with locale=* is required.
        $locale = $this->getLocaleFromInput($locale);

        if (\array_key_exists($locale, $value)) {
            return $value[$locale];
        }

        // If a field is not localized, it means that there are no values besides
        // $value[$defaultLocale], so because that check has already happened, we know
        // we're trying to access an invalid locale which is not correctly set.
        if (!$field->isLocalized()) {
            throw new \InvalidArgumentException(\sprintf(
                'Trying to access the non-localized field "%s" on content type "%s" using the non-default locale "%s".',
                $field->getName(),
                $this->sys->getContentType()->getName(),
                $locale
            ));
        }

        // If we reach this point, it means:
        // * the field is localized
        // * we're trying to get a non-default locale
        // * the entry was not built using a specific locale (i.e. all locales for a field are available)
        // Therefore, we can inspect the fallback chain for a suitable locale.
        $locale = $this->walkFallbackChain($value, $locale, $this->sys->getEnvironment());

        if ($locale) {
            return $value[$locale];
        }

        return 'Array' === $field->getType() ? [] : null;
    }