Uncatchable Unhandled Exception

I had some Unhandled Exceptions in my app so in the latest release I added a try/catch:

function getConfig(key as PropertyKeyType) as PropertyValueType or Null {
    var val;
    try {
        val = Properties.getValue(key);
    } catch (e) {
        val = null;
        logException(key, val, e as Exception);
    }
    return val;
}

So how come I still get Unhandled exception in line 4?