servers.get(search_term) might raise some exceptions which needs to be handled here. Plus you are overriding the get_server(arg) method from fog/service.rb here. If you are overriding on purpose then you can use some exception handling except( Excon::Errors::BadRequest ) or you can rename the method.

https://github.com/opscode/knife-cloud/blob/master/lib/chef/knife/cloud/fog/service.rb#L137