Nelmio\SecurityBundle\ContentSecurityPolicy\DirectiveSet::canNotBeFallbackedByDefault PHP Method

    private function canNotBeFallbackedByDefault($name, $value)
    {
        if ($name === 'default-src') {
            return true;
        }
        // Only source-list can be fallbacked by default
        if (self::$directiveNames[$name] !== self::TYPE_SRC_LIST) {
            return true;
        }
        // let's fallback if directives are strictly equals
        return $value !== $this->getDirective('default-src');
    }