title: Not able to reference Firestore document path
body: <p>I need to add user record using collection path. I'm using following code:</p>
  
  <pre><code>var todays_date : String = ""
  let dateFormatter : DateFormatter = DateFormatter()
          dateFormatter.dateFormat = "MMddyyyy"
          let date = Date()
          todays_date = dateFormatter.string(from: date)
  
  docRef = Firestore.firestore().document("userData/scriptureTracking/users/" + user_id.replacingOccurrences(of: " ", with: "_") + "/" + todays_date)
  
  docRef.setData(dataToSave) { (error) in
                  if let error = error {
                      print("CloudFirestore Got error: \(error.localizedDescription)")
                  } else {
                      print("CloudFirestore: Data has been saved!")
                  }
  }
  </code></pre>
  
  <p>Somehow it is not able to reference it properly. It is crashing out at this line. If I remove last backslash and 'todays_date' then it is working fine (Saving data using docRef). But I need both 'user_id' and 'todays_date' for querying later. Any idea?</p>