fix: Make dropletIds field for DigitalOceanVolume optional

lib/logic/models/json/digital_ocean_server_info.dart

@@ -15,7 +15,7 @@ class DigitalOceanVolume {
   final String name;
 
   @JsonKey(name: 'droplet_ids')
-  final List<int> dropletIds;
+  final List<int>? dropletIds;
 
   @JsonKey(name: 'size_gigabytes')
   final int sizeGigabytes;

lib/logic/models/json/digital_ocean_server_info.g.dart

@@ -11,7 +11,7 @@ DigitalOceanVolume _$DigitalOceanVolumeFromJson(Map<String, dynamic> json) =>
       json['id'] as String,
       json['name'] as String,
       json['size_gigabytes'] as int,
-      (json['droplet_ids'] as List<dynamic>).map((e) => e as int).toList(),
+      (json['droplet_ids'] as List<dynamic>?)?.map((e) => e as int).toList(),
     );
 
 Map<String, dynamic> _$DigitalOceanVolumeToJson(DigitalOceanVolume instance) =>

lib/logic/providers/server_providers/digital_ocean.dart

@@ -647,7 +647,9 @@ class DigitalOceanServerProvider extends ServerProvider {
           name: volumeName,
           sizeByte: rawVolume.sizeGigabytes * 1024 * 1024 * 1024,
           serverId:
-              rawVolume.dropletIds.isNotEmpty ? rawVolume.dropletIds[0] : null,
+              (rawVolume.dropletIds != null && rawVolume.dropletIds!.isNotEmpty)
+                  ? rawVolume.dropletIds![0]
+                  : null,
           linuxDevice: 'scsi-0DO_Volume_$volumeName',
           uuid: rawVolume.id,
         );