diff --git a/src/alohalytics.h b/src/alohalytics.h
index 3c8906e..f46719e 100644
--- a/src/alohalytics.h
+++ b/src/alohalytics.h
@@ -80,7 +80,9 @@ class Stats final {
   // - Gzipped.
   // - Saved as out_archive for easier post-processing (e.g. uploading).
   // - Deleted.
-  void GzipAndArchiveFileInTheQueue(const std::string & in_file, const std::string & out_archive);
+  void GzipAndArchiveFileInTheQueue(const std::string & in_file, const std::string & out_archive) const;
+  std::string GzipInMemoryBuffer(const std::string & buffer) const;
+  std::string SerializeUniqueClientId() const;
 
   void LogEventImpl(AlohalyticsBaseEvent const & event, uint32_t channels_mask);
 
diff --git a/src/android/java/org/alohalytics/Statistics.java b/src/android/java/org/alohalytics/Statistics.java
index a75565d..488fc24 100644
--- a/src/android/java/org/alohalytics/Statistics.java
+++ b/src/android/java/org/alohalytics/Statistics.java
@@ -143,6 +143,7 @@ public static void setup(String[] serverUrls, final Context context) {
         storagePath = context.getFilesDir().getAbsolutePath() + "/Alohalytics" + i + "/";
       // Native code expects valid existing writable dir.
       (new File(storagePath)).mkdirs();
+      paths[i] = storagePath;
     }
 
     String[] urls = new String[serverUrls.length];
diff --git a/src/cpp/alohalytics.cc b/src/cpp/alohalytics.cc
index dd737d8..86d2bb1 100644
--- a/src/cpp/alohalytics.cc
+++ b/src/cpp/alohalytics.cc
@@ -82,7 +82,7 @@ void Stats::Enable() {
   enabled_ = true;
 }
 
-void Stats::GzipAndArchiveFileInTheQueue(const std::string & in_file, const std::string & out_archive) {
+void Stats::GzipAndArchiveFileInTheQueue(const std::string & in_file, const std::string & out_archive) const {
   std::string encoded_unique_client_id;
   if (unique_client_id_.empty()) {
     LOG_IF_DEBUG(
@@ -91,11 +91,7 @@ void Stats::GzipAndArchiveFileInTheQueue(const std::string & in_file, const std:
   } else {
     // Pre-calculation for special ID event.
     // We do it for every archived file to have a fresh timestamp.
-    AlohalyticsIdEvent event;
-    event.id = unique_client_id_;
-    std::ostringstream ostream;
-    { cereal::BinaryOutputArchive(ostream) << std::unique_ptr<AlohalyticsBaseEvent, NoOpDeleter>(&event); }
-    encoded_unique_client_id = ostream.str();
+    encoded_unique_client_id = SerializeUniqueClientId();
   }
   LOG_IF_DEBUG("Archiving", in_file, "to", out_archive);
   // Append unique installation id in the beginning of each archived file.
@@ -132,6 +128,22 @@ void Stats::GzipAndArchiveFileInTheQueue(const std::string & in_file, const std:
     LOG_IF_DEBUG("CRITICAL ERROR: std::remove", in_file, "has failed with error", result, "and errno", errno);
   }
 }
+  
+std::string Stats::GzipInMemoryBuffer(const std::string & buffer) const {
+  if (unique_client_id_.empty()) {
+    LOG_IF_DEBUG("Warning: unique client id was not set in GzipInMemoryBuffer,"
+                 "statistics will be completely anonymous and hard to process on the server.");
+  }
+  return alohalytics::Gzip(SerializeUniqueClientId() + buffer);
+}
+  
+std::string Stats::SerializeUniqueClientId() const {
+  AlohalyticsIdEvent event;
+  event.id = unique_client_id_;
+  std::ostringstream ostream;
+  { cereal::BinaryOutputArchive(ostream) << std::unique_ptr<AlohalyticsBaseEvent, NoOpDeleter>(&event); }
+  return ostream.str();
+}
 
 Stats & Stats::Instance() {
   static Stats alohalytics;
@@ -282,7 +294,7 @@ void Stats::Upload(const TFileProcessingFinishedCallback & upload_finished_callb
           r = *upload_result;
         }
       }
-      if (need_notify)
+      if (upload_finished_callback && need_notify)
         upload_finished_callback(r);
     };
     for (auto & c : channels_) {
@@ -308,7 +320,7 @@ bool Stats::UploadFileImpl(const std::string & upload_url, bool file_name_in_con
     if (file_name_in_content) {
       request.set_body_file(content, kAlohalyticsHTTPContentType, "POST", "gzip");
     } else {
-      request.set_body_data(alohalytics::Gzip(content), kAlohalyticsHTTPContentType, "POST", "gzip");
+      request.set_body_data(GzipInMemoryBuffer(content), kAlohalyticsHTTPContentType, "POST", "gzip");
     }
     const bool uploadSucceeded = request.RunHTTPRequest() && 200 == request.error_code() && !request.was_redirected();
     LOG_IF_DEBUG("RunHTTPRequest has returned code", request.error_code(),
@@ -351,7 +363,7 @@ void Stats::CollectBlobsToUpload(bool delete_files, TGetBlobResultCallback resul
           result->push_back(std::move(buffer));
         } else {
           std::lock_guard<std::mutex> lock(collect_mutex_);
-          result->push_back(alohalytics::Gzip(content));
+          result->push_back(GzipInMemoryBuffer(content));
         }
         return true;
       } catch (const std::exception & ex) {