Swift compiler does not detect the `try` expression given to the Result initializer unless broken up into its own expression

swift_warning_issue.swift

// warning: 'catch' block is unreachable because no errors are thrown in 'do' block
public func requestJSON<ModelType: MTLModel>(target: CocoaBlocAPI) -> SignalProducer<ModelType, NSError> {
    return tryGetJSONObjectForKey(requestJSON(target), key: "data")
        .attemptMap { (value: [NSObject:AnyObject]) -> Result<ModelType, NSError> in
            do {
                return Result(try MTLJSONAdapter.modelOfClass(ModelType.self, fromJSONDictionary: value) as! ModelType)
            }
            catch let error as NSError {
                return .Failure(error)
            }
        }
}

// no warnings
public func requestJSON<ModelType: MTLModel>(target: CocoaBlocAPI) -> SignalProducer<ModelType, NSError> {
    return tryGetJSONObjectForKey(requestJSON(target), key: "data")
        .attemptMap { (value: [NSObject:AnyObject]) -> Result<ModelType, NSError> in
            do {
                let p = try MTLJSONAdapter.modelOfClass(ModelType.self, fromJSONDictionary: value) as! ModelType
                return Result(p)
            }
            catch let error as NSError {
                return .Failure(error)
            }
        }
}