Fixes 1.9.3 compatibility issue with NilClass#to_h.

1.9.3(I tested with ruby-1.9.3-p547 specifically) has this behavior:
```ruby
nil.respond_to? :to_h #=> false
```
2.0.0 and up have the opposite behavior:
```ruby
nil.respond_to? :to_h #=> true
```

This was in turn causing the output to b incorrect with regard to defined separators.