'NSInvalidArgumentException', reason: '*** -propertyForKey: only defined for abstract class

[konomae]

Hi

I found this exception in Crashlytics crash logs from my production app.
I can reproduce and paste it bellow. But I cannot find how to fix it.
So, I just report this.

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -propertyForKey: only defined for abstract class.  Define -[_TtCV6APIKit31MultipartFormDataBodyParameters20MultipartInputStream propertyForKey:]!'

• Xcode 8.3.3
• iOS 10.3 SDK
• iPhone Plus (iOS 10.3 simulator)

import UIKit
import APIKit

protocol HttpBinRequest: Request {

}

extension HttpBinRequest {
    var baseURL: URL {
        return URL(string: "https://httpbin.org")!
    }
}

struct PostRequest: HttpBinRequest {
    typealias Response = Any

    var method: HTTPMethod {
        return .post
    }

    var path: String {
        return "/post"
    }

    var bodyParameters: BodyParameters? {
        let p = try! MultipartFormDataBodyParameters.Part(
            value: "value",
            name: "name"
        )

        return MultipartFormDataBodyParameters(parts: [p], entityType: .inputStream)
    }

    func response(from object: Any, urlResponse: HTTPURLResponse) throws -> Response {
        return object
    }
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        let request = PostRequest()

        Session.send(request) { result in
            print(result)
            switch result {
            case .success(let response):
                print(response)
            case .failure(let error):
                print("error: \(error)")
            }
        }
    }
}

[konomae]

Minimize test case

func testReproduceIssue250() {
    struct PostRequest: Request {
        let baseURL = URL(string: "https://httpbin.org")!
        let method: HTTPMethod = .post
        let path = "/post"
        let bodyParameters: BodyParameters? = MultipartFormDataBodyParameters(
            parts: [],
            entityType: .inputStream
        )

        func response(from object: Any, urlResponse: HTTPURLResponse) throws -> Any {
            return object
        }
    }

    let expectation = self.expectation(description: #function)
    let request = PostRequest()
    Session.send(request) { result in
        switch result {
        case .success:
            expectation.fulfill()
        case .failure:
            XCTFail()
        }
    }

    wait(for: [expectation], timeout: 3.0)
}

'NSInvalidArgumentException', reason: '*** -propertyForKey: only defined for abstract class.  Define -[_TtCV6APIKit31MultipartFormDataBodyParameters20MultipartInputStream propertyForKey:]!'