Remove confusing no-op

This line previously always set the (unused) local variable body to nil.

I assume it meant to read `self.body = nil if body.nil?` however
`body.nil?` cannot happen as the previous line would crash.

Closer inspection reveals that the initialize method calls either
init_with_string or init_with_hash, both of which eventually set the
body to non-nil.
Merge pull request #499 from ConradIrwin/remove-no-op

Remove confusing no-op