title: Firestore - Exception 'FIRInvalidArgumentException', reason: 'Unsupported type: _SwiftValue'
body: <blockquote>
    <p>Terminating app due to uncaught exception
    'FIRInvalidArgumentException', reason: 'Unsupported type: _SwiftValue'</p>
  </blockquote>
  
  <p>I' trying to create or update document in Firestore and getting that error. </p>
  
  <pre><code>DispatchQueue.main.asyncAfter(deadline: .now() + 0.2, execute: {
  
           let docData: [String: Any] = [
                "firebase_buyer_id": "222", // todo - set buyer id correctly
                "firebase_seller_id": "String(describing: self!.ad.ownerId)",
                "reference_object": [        
                     "reference_object_id": "testing_id",
                     "last_updated_time": Timestamp(date: Date()),
                     "chat_item_list": [
                                      {
                                          [
                                              "chat_id": "12", // set chat id
                                              "owner_id": "222",
                                              "time_stamp": Timestamp(date: Date()),
                                              "message": "testing message - hi, message send successfully"
                                          ]
                                      }
                    ]
               ]
            ]
  
            self!.db.collection((self?.collectionName)!).document((self?.refId)!).setData(docData){ err in
                    if let err = err {
                          print("Error writing document: \(err)")
                    } else {
                          print("Document successfully written!")
                    }
             }
   })
  </code></pre>