Gotchas: rspec expect change gives: "nil is not a symbol"

*sigh* There's a small, but meaningful difference between:

   expect {
     my_thing.do_stuff
   }.to change(my_thing.my_value).to(some_value)

and

   expect {
     my_thing.do_stuff
   }.to change{my_thing.my_value}.to(some_value)

(note the braces on the last line...)