Merge branch 'Issue/1913-ModificationsResourceMetadata' into 'dev'

Issue/1913 modifications resource metadata

See merge request !157

src/Database/Models/ResourceModel.cs

@@ -333,6 +333,8 @@ namespace Coscine.Database.Models
             {
                 resource.LicenseId = resourceObject.License.Id;
             }
+            else
+                resource.LicenseId = null;
 
             // the application profile can not be altered after creation
             // resource.ApplicationProfile = resourceObject.ApplicationProfile;