Fixes wacky crashing bug involving a nil parameter being handed to `+[NSString stringWithFormat:]`
Fixes wacky crashing bug involving a nil parameter being handed to `+[NSString stringWithFormat:]`

This is especially weird to me given that I thought this method was perfectly capable of handling nil values, but what do I know?

cathy810218/onebusaway-iphone,OneBusAway/onebusaway-iphone,ualch9/onebusaway-iphone,themonki/onebusaway-iphone,OneBusAway/onebusaway-iphone,themonki/onebusaway-iphone,themonki/onebusaway-iphone,themonki/onebusaway-iphone,OneBusAway/onebusaway-iphone,themonki/onebusaway-iphone,ualch9/onebusaway-iphone,cathy810218/onebusaway-iphone,OneBusAway/onebusaway-iphone,ualch9/onebusaway-iphone,OneBusAway/onebusaway-iphone,cathy810218/onebusaway-iphone,ualch9/onebusaway-iphone,ualch9/onebusaway-iphone,cathy810218/onebusaway-iphone