diff --git a/td/telegram/files/FileLocation.h b/td/telegram/files/FileLocation.h
index 63ba32e15..3e54f5fa5 100644
--- a/td/telegram/files/FileLocation.h
+++ b/td/telegram/files/FileLocation.h
@@ -269,7 +269,7 @@ class FullRemoteFileLocation {
   static constexpr int32 FILE_REFERENCE_FLAG = 1 << 25;
   bool web_location_flag_{false};
   DcId dc_id_;
-  std::string file_reference_;
+  string file_reference_;
   enum class LocationType : int32 { Web, Photo, Common, None };
   Variant<WebRemoteFileLocation, PhotoRemoteFileLocation, CommonRemoteFileLocation> variant_;
 
@@ -395,7 +395,7 @@ class FullRemoteFileLocation {
     }
   }
   void clear_file_reference() {
-    file_reference_ = "";
+    file_reference_.clear();
   }
 
   bool delete_file_reference(Slice bad_file_reference) {
diff --git a/td/telegram/net/DcId.h b/td/telegram/net/DcId.h
index 819baded4..d61546d17 100644
--- a/td/telegram/net/DcId.h
+++ b/td/telegram/net/DcId.h
@@ -88,8 +88,12 @@ class DcId {
 
 inline StringBuilder &operator<<(StringBuilder &sb, const DcId &dc_id) {
   sb << "DcId{";
-  if (dc_id.is_empty()) {
+  if (dc_id == DcId::invalid()) {
+    sb << "invalid";
+  } else if (dc_id == DcId()) {
     sb << "empty";
+  } else if (dc_id.is_empty()) {
+    sb << "is_empty";
   } else if (dc_id.is_main()) {
     sb << "main";
   } else {