Argo doesn't work with subclass (Swift 1.2 AND 2.0)

Argo-decode-classes.swift

import XCTest
import Argo
import Runes

class SuperClass {
  let something: String

  init(something: String) {
    self.something = something
  }
}

extension SuperClass: Decodable {
  static func create(something: String) -> SuperClass {
    return SuperClass(something: something)
  }

  static func decode(j: JSON) -> Decoded<SuperClass> {
    return SuperClass.create
      <^> j <| "something"
  }
}

class SubClass: SuperClass {
  let someOtherThing: String

  init(something: String, someOtherThing: String) {
    self.someOtherThing = someOtherThing
    super.init(something: something)
  }
}

//extension SubClass: Decodable {
// ERROR in the line above:
// * Swift 1.2: Type 'SubClass' does not conform to protocol 'Decodable'
// * Swift 2.0: Redundant conformance of 'SubClass' to protocol 'Decodable'

extension SubClass {
  static func create(something: String)(someOtherThing: String) -> SubClass {
    return SubClass(something: something, someOtherThing: someOtherThing)
  }

  static func decode(j: JSON) -> Decoded<SubClass> {
    return SubClass.create
      <^> j <| "something"
      <*> j <| "some_other_thing"
  }
}

class DecodingTests: XCTestCase {
  func testDecodingSuperClass() {
    let model: SuperClass? = JSONFromFile("super_class") >>- decode

    XCTAssert(model != nil)
    XCTAssert(model?.something == "Something")
  }

  func testDecodingSubClass() {
    // ERROR in the line below comments
    // for both Swift 1.2 and 2.0:
    // Could not find an overload that accepts the supplied argument
    let model: SubClass? = JSONFromFile("sub_class") >>- decode

    XCTAssert(model != nil)
    XCTAssert(model?.something == "Something")
    XCTAssert(model?.someOtherThing == "Some other thing")
  }
}

sub_class.json

{
  "something": "Something",
  "some_other_thing": "Some other thing"
}

super_class.json

{
  "something": "Something"
}