Check if oauth2_key_group_filter is empty before exploding it.
Else isGroupInFilter does not catch _if (empty($filter))_ because the $filter array contains 1.
Right now if you don't set a Groups Key in the integration configuration then $this->getKey() will log "PHP Notice: Undefined index: " because it's being asked to look for a blank key. This commit first checks whether the key is set before passing it to getKey() to prevent this Notice.
for example some OAuth2 provider provide multiple emails like this:
```
{
"_id": "aobEdbYhXfu5hkeqG",
"name": "Example User",
"emails": [
{
"address": "example1@example.com",
"primary": true
},
{
"address": "example2@example.com",
"primary": false
}
],
"status": "offline",
"statusConnection": "offline",
"username": "example",
"utcOffset": 0,
......
```
we need get email address for email map in kanboard.
this patch use `.` as separator to get value from nested structure.
in this example we can use `emails.0.address` as key name to get first
email address.
cupcakearmy
Christoph Daniel Miksche
Byron Marohn
Omar Ramos
mildis
Frédéric Guillot
Tilo
RussellAult
renothing
Sascha Kühndel
Felix Gustavsson