src/Modules/Assets/AssetsCollection.php
public function getLastModified()
    {
        $last_modified = 0;
        foreach ($this->assets as $asset) {
            if (!file_exists($asset->getPath())) {
                throw new \RuntimeException(sprintf('The source file "%s" doesn`t exists: ', $asset->getURL()));
            }

            $asset_last_modified = filemtime($asset->getPath());
            if ($asset_last_modified > $last_modified) {
                $last_modified = $asset_last_modified;
            }
        }
        return $last_modified;
    }
public function getLastModified()
    {
        $last_modified = 0;
        foreach ($this->assets as $asset) {
            if (!file_exists($asset->getPath())) {
                throw new \RuntimeException(sprintf('The source file "%s" doesn`t exists: ', $asset->getURL()));
            }

            $asset_last_modified = filemtime($asset->getPath());
            if ($asset_last_modified > $last_modified) {
                $last_modified = $asset_last_modified;
            }
        }
        return $last_modified;
    }
@return integer

@throws \RuntimeException