Logger: handle nullptr.

logger/Logger.cxx

@@ -470,7 +470,7 @@ void Logger::RemoveCustomSink(const string& key)
     }
 }
 
-ostringstream& Logger::Log()
+Logger& Logger::Log()
 {
     char tsstr[32];
     if (!strftime(tsstr, sizeof(tsstr), "%H:%M:%S", localtime(&(fMetaData.timestamp))))
@@ -522,7 +522,19 @@ ostringstream& Logger::Log()
         fColorOut << " ";
     }
 
-    return fContent;
+    return *this;
+}
+
+Logger& Logger::operator<<(ios_base& (*manip) (ios_base&))
+{
+    fContent << manip;
+    return *this;
+}
+
+Logger& Logger::operator<<(ostream& (*manip) (ostream&))
+{
+    fContent << manip;
+    return *this;
 }
 
 Logger::~Logger() noexcept(false)

logger/Logger.h

@@ -144,7 +144,35 @@ class Logger
     static void AddCustomSink(const std::string& key, const std::string& severityStr, std::function<void(const std::string& content, const LogMetaData& metadata)> sink);
     static void RemoveCustomSink(const std::string& key);
 
-    std::ostringstream& Log();
+    Logger& Log();
+
+    template<typename T>
+    Logger& operator<<(const T& t)
+    {
+        fContent << t;
+        return *this;
+    }
+
+    // overload for char* to make sure it is not nullptr
+    Logger& operator<<(const char* cptr)
+    {
+        if (cptr != nullptr) {
+            fContent << cptr;
+        }
+        return *this;
+    }
+
+    // overload for char* to make sure it is not nullptr
+    Logger& operator<<(char* cptr)
+    {
+        if (cptr != nullptr) {
+            fContent << cptr;
+        }
+        return *this;
+    }
+
+    Logger& operator<<(std::ios_base& (*manip) (std::ios_base&));
+    Logger& operator<<(std::ostream& (*manip) (std::ostream&));
 
     static const std::unordered_map<std::string, Verbosity> fVerbosityMap;
     static const std::unordered_map<std::string, Severity> fSeverityMap;