Attempt to workaround problem reported about empty plc.xml after unrelated crash. Now, if etree model is corrupted in a way tostring() would generate an empty string, exception prevents saving.
{
"ID": "wamptest",
"active": true,
"protocolOptions": {
"autoPingInterval": 60,
"autoPingTimeout": 20
},
"realm": "Automation",
"url": "ws://127.0.0.1:8888"
}