optionals handling fix

Sources/Decoder.swift

@@ -73,6 +73,14 @@ extension AnyDecoder {
         }
     }
 
+    public func decode<T: AnyDecodable>() throws -> T? {
+        return try decode(transform: T.init)
+    }
+
+    public func decode<T>(transform: (AnyDecoder) throws ->T? ) throws -> T? {
+        return try transform(self)
+    }
+
     //MARK:- handle object decode
 
     private func handleObjectDecode<T, U>(key: String, action: (T) throws -> U) throws -> U {

Tests/AnyCoderTests/AnyCoderTests.swift

@@ -475,6 +475,25 @@ class AnyCoderTests: XCTestCase {
         }
     }
 
+    func testOptionalInit() {
+
+        struct TestUrl: AnyDecodable {
+            let url: URL?
+
+            init?(decoder: AnyDecoder) throws {
+                return nil
+            }
+        }
+
+        let json: [String: Any] = ["url": NSNull()]
+        do {
+            _ = try json.decode() as TestUrl?
+        }
+        catch {
+            XCTFail("Should haven't thrown")
+        }
+    }
+
     func testFailedOptionalException() {
 
         struct TestUrl: AnyDecodable {