Add content to media: localFilePath cannot be null

@KalturaFan ,
Sorry for the confusion, but the log was pretty clearly stating this is due to permission.
For more background: It's intentionally blocked as we don't want to allow every user to upload files by specifying paths of files in the server. That could become a security risk if it was allowed.
As such this resource type is only allowed for partner -1 (the system wide admin user).