wrapped a failing call to concat on empty string in lib/spree_active_shi...

...pping/engine.rb, line 35. my system had no app.config.spree.calculators.shipping_methods.

Until I wrapped this call, I was unable to run migrations installed via railties, or boot Webrick. 

That commit message should actually read: "wrapped a failing call to concat on NIL in lib/spree_active_shipping/engine.rb, line 35. my system had no app.config.spree.calculators.shipping_methods." 

Sorry for the inaccuracy.