Swift 1.2 : Confusing error message for closures that do not return value

gistfile1.swift

import UIKit
import Foundation

//set up
extension Array {
    func filterMap<U>(transform: (T) -> U?) -> [U] {
        var mapped = [U]()
        for item in self {
            if let unwrapped = transform(item) {
                mapped.append(unwrapped)
            }
        }
        return mapped
    }
}

var array : [String] = []
/*
  no error message as expected
*/
let transformedReturnsValue : [Int] = array.filterMap({
    (data: String) -> Int? in
    return 1
})

/*
 If the closure has no statements in it you
 get the helpful error message :
 
 "Missing return in a closure expected to return 'Int?'"
*/
let transformedEmptyClosure : [Int] = array.filterMap({
    (data: String) -> Int? in
    //return 1
})

/*
 If the closure has statements in it but no 
 return you get the confusing error message :

 Cannot invoke 'filterMap' with an argument list of type '((String) -> Int?)'
*/
let transformedNoReturn : [Int] = array.filterMap({
    (data: String) -> Int? in
    println("foo")
})