According to the documentation of this method:

Return Value: An NSURL object initialized with path, or nil if path is zero-length.

But the method is marked as returning a non-optional.

And you can verify that this is what's going on by using the code

let url: NSURL? = NSURL(fileURLWithPath: "")
print(url)

(this trick of explicitly typing the variable as an optional lets you handle any case where an Obj-C method is marked as returning a non-optional value but is actually returning nil).

Given Kevin's diagnosis, this isn't a Swift issue; it should be filed against Apple Foundation in Radar.

Please forgive my ignorance, but I couldn't find any category resembling Apple Foundation in bugreport.apple.com. So I'll leave it to anyone who knows how to (file it against Apple Foundation in Radar).

@jepers File it against either "iOS SDK" or "OS X SDK".

OK, done: 25118040