I agree with @mowings.  We probably want one of the following: 

```ruby
when message
...
else
  if message.respond_to? :to_s
    hash.merge!( '@message' => message.to_s)
  else
    hash.merge!( '@message' => message.inspect)
  end
end
```

or:
```ruby
when message
...
else
  raise "Unexpected log message type: #{message.class.name}"
end
```