this is not good ruby way to do that:

```ruby
[first_name, last_name].join(' ') if first_name && last_name
```

or

```ruby
(first_name && last_name) ? [first_name, last_name].join(' ') : nil
```

i prefer first one, if you need do it in that way, best will be 

```ruby
return unless first_name || last_name
[first_name, last_name].join(' ')
```