Json_encode error

Fresh install on debian 9 (php7.0)

at first I got error:

PHP Fatal error: Interface ‘JsonSerializable’ not found in /usr/share/pydio/plugins/core.access/src/Filter/AJXP_Permission.php on line 34

I made ugly hack: added several lines at the beginning of index.php
if (!interface_exists(‘JsonSerializable’)) {
interface JsonSerializable
{
public function jsonSerialize();
}
}

After that I got one more error:

PHP Fatal error: Uncaught Error: Call to undefined function Pydio\Core\PluginFramework\json_encode() in /usr/share/pydio/core/src/pydio/Core/PluginFramework/Plugin.php:989\nStack trace:\n#0 /usr/share/pydio/core/src/pydio/Core/PluginFramework/Plugin.php(753): Pydio\Core\PluginFramework\Plugin->exposeConfigInManifest(‘SKIP_USER_HISTO…’, true)\n#1 /usr/share/pydio/core/src/pydio/Core/PluginFramework/PluginsService.php(576): Pydio\Core\PluginFramework\Plugin->loadConfigs(Array)\n#2 /usr/share/pydio/core/src/pydio/Core/PluginFramework/PluginsService.php(157): Pydio\Core\PluginFramework\PluginsService->softLoad(‘core.conf’, Array)\n#3 /usr/share/pydio/core/src/pydio/Core/PluginFramework/PluginsService.php(809): Pydio\Core\PluginFramework\PluginsService::cachePluginSoftLoad()\n#4 /usr/share/pydio/core/src/pydio/Core/PluginFramework/PluginsService.php(203): Pydio\Core\PluginFramework\PluginsService->getDetectedPlugins()\n#5 /usr/share/pydio/core/src/pydio/Core/Services/ConfService.php(392): Pydio\Core\PluginFramework\PluginsService::getI in /usr/share/pydio/core/src/pydio/Core/PluginFramework/Plugin.php on line 989

How to fix it?

Hi,
could you tell me what pydio version you installed, php version (7 i believe ) and your webserver.