Unable to resolve NULL driver Lumen 5.6 - email

Question

In a development environment all works fine.
But in production, Lumen returns me Unable to resolve NULL driver [Illuminate\Mail\TransportManager]
After some research, I discovered that when I debug $app:
In both mode, all configurations is loaded.
["loadedConfigurations":protected]=>
array(5) {
["mail"]=> bool(true)
//other keys ...
}
But:
In development, the debug returns all my Lumen's configuration:
array(6) {
["app"]=>
*RECURSION*
["Laravel\Lumen\Application"]=>
*RECURSION*
["path"]=>
string(17) "/var/www/html/app"
["config"]=>
object(Illuminate\Config\Repository)#5 (1) {
["items":protected]=>
array(5) {
//all keys ...
}
On production (share hosting server), the debug doesn't return configuration's keys :
array(6) {
["app"]=>
*RECURSION*
["Laravel\Lumen\Application"]=>
*RECURSION*
["path"]=>
string(11) "/htdocs/app"
["config"]=>
object(Illuminate\Config\Repository)#5 (1) {
["items":protected]=>
array(0) {
//no keys
}
}
This is the reason for which Lumen doesn't find driver for the mailing.
Now I can't explain why Lumen ignores my configuration. Someone knows?
Thanks you,

Answer 1

I just found the reason of this problem.
In production, the server is case sensitive.
My directory was /Config and it need /config in lower case