diff --git a/td/generate/DoxygenTlDocumentationGenerator.php b/td/generate/DoxygenTlDocumentationGenerator.php
index 8f727a047..5acffadf9 100644
--- a/td/generate/DoxygenTlDocumentationGenerator.php
+++ b/td/generate/DoxygenTlDocumentationGenerator.php
@@ -127,6 +127,7 @@ class DoxygenTlDocumentationGenerator extends TlDocumentationGenerator
         return empty($tline) || $tline[0] === '}' || $tline === 'public:' || strpos($line, '#pragma ') === 0 ||
             strpos($line, '#include <') === 0 || strpos($tline, 'return ') === 0 || strpos($tline, 'namespace') === 0 ||
             preg_match('/class [A-Za-z0-9_]*;/', $line) || $tline === 'if (value == nullptr) {' ||
+            strpos($tline, 'result += ') === 0 || strpos($tline, 'result = ') || strpos($tline, ' : values') ||
             strpos($line, 'JNIEnv') || strpos($line, 'jfieldID') || $tline === 'virtual ~Object() {' ||
             $tline === 'virtual void store(TlStorerToString &s, const char *field_name) const = 0;';
     }
@@ -294,7 +295,7 @@ EOT
 
         $this->addDocumentation('std::string to_string(const BaseObject &value);', <<<EOT
 /**
- * Returns a string representation of the TDLib API object.
+ * Returns a string representation of a TDLib API object.
  * \\param[in] value The object.
  * \\return Object string representation.
  */
@@ -303,12 +304,22 @@ EOT
 
         $this->addDocumentation('std::string to_string(const object_ptr<T> &value) {', <<<EOT
 /**
- * Returns a string representation of the TDLib API object.
+ * Returns a string representation of a TDLib API object.
  * \\tparam T Object type, auto-deduced.
  * \\param[in] value The object.
  * \\return Object string representation.
  */
 EOT
+);
+
+        $this->addDocumentation('std::string to_string(const std::vector<object_ptr<T>> &values) {', <<<EOT
+/**
+ * Returns a string representation of a list of TDLib API objects.
+ * \\tparam T Object type, auto-deduced.
+ * \\param[in] values The objects.
+ * \\return Objects string representation.
+ */
+EOT
 );
 
         $this->addDocumentation('  void store(TlStorerToString &s, const char *field_name) const final;', <<<EOT
diff --git a/td/generate/tl_writer_h.cpp b/td/generate/tl_writer_h.cpp
index d7e701cbe..cb9532da9 100644
--- a/td/generate/tl_writer_h.cpp
+++ b/td/generate/tl_writer_h.cpp
@@ -94,6 +94,20 @@ std::string TD_TL_writer_h::gen_output_begin() const {
          "  }\n"
          "\n"
          "  return to_string(*value);\n"
+         "}\n\n"
+
+         "template <class T>\n"
+         "std::string to_string(const std::vector<object_ptr<T>> &values) {\n"
+         "  std::string result = \"{\\n\";\n"
+         "  for (const auto &value : values) {\n"
+         "    if (value == nullptr) {\n"
+         "      result += \"null\\n\";\n"
+         "    } else {\n"
+         "      result += to_string(*value);\n"
+         "    }\n"
+         "  }\n"
+         "  result += \"}\\n\";\n"
+         "  return result;\n"
          "}\n\n";
 }
 
diff --git a/td/telegram/GroupCallManager.cpp b/td/telegram/GroupCallManager.cpp
index bcc712a43..9eec77eb9 100644
--- a/td/telegram/GroupCallManager.cpp
+++ b/td/telegram/GroupCallManager.cpp
@@ -927,7 +927,7 @@ void GroupCallManager::on_update_group_call_participants(
         group_call->participant_count += diff;
         if (group_call->participant_count < 0) {
           LOG(ERROR) << "Participant count became negative in " << input_group_call_id << " from "
-                     << group_call->dialog_id;
+                     << group_call->dialog_id << " after applying " << to_string(participants);
           group_call->participant_count = 0;
         }
         update_group_call_dialog(group_call, "on_update_group_call_participants");