src/Resource/Entry.php
private function getFieldWithId(string $name, string $locale = null)
    {
        if ('Id' !== \mb_substr($name, -2)) {
            return null;
        }

        $field = $this->sys->getContentType()->getField(\mb_substr($name, 0, -2), true);
        if (!$field) {
            return null;
        }

        if ('Link' !== $field->getType() && ('Array' !== $field->getType() || 'Link' !== $field->getItemsType())) {
            return null;
        }

        $value = $this->getUnresolvedField($field, $locale);
        if ($value instanceof Link) {
            return $value->getId();
        }

        return \array_map(function (Link $link) {
            return $link->getId();
        }, $value);
    }
private function getFieldWithId(string $name, string $locale = null)
    {
        if ('Id' !== \mb_substr($name, -2)) {
            return null;
        }

        $field = $this->sys->getContentType()->getField(\mb_substr($name, 0, -2), true);
        if (!$field) {
            return null;
        }

        if ('Link' !== $field->getType() && ('Array' !== $field->getType() || 'Link' !== $field->getItemsType())) {
            return null;
        }

        $value = $this->getUnresolvedField($field, $locale);
        if ($value instanceof Link) {
            return $value->getId();
        }

        return \array_map(function (Link $link) {
            return $link->getId();
        }, $value);
    }
Checks whether the given $name parameter corresponds to an attempt
of fetching the ID of a link (or array of links).

@param string      $name
@param string|null $locale

@return string|string[]|null Returns null if $name is not a valid field ID string