diff --git a/common/json/json.cpp b/common/json/json.cpp
index 70c0ff2..e8ae93f 100644
--- a/common/json/json.cpp
+++ b/common/json/json.cpp
@@ -514,7 +514,7 @@ bool json::set_value(const char* key, double val)
 
 	return true;
 }
-bool json::set_value(const char* key, std::string val)
+bool json::set_value(const char* key, const char* val)
 {
 	if (type_ != VAL_TYPE_OBJECT)
 		return false;
@@ -526,12 +526,12 @@ bool json::set_value(const char* key, std::string val)
 		child->clear();
 		child->type_ = VAL_TYPE_STRING;
 		child->key() = key ? key : "";
-		child->strval_ = val;
+		child->strval_ = val ? val : "";
 		child->release();
 	}
 	else
 	{
-		child = new json(key, val.c_str());
+		child = new json(key, val);
 		arr_val_.push_back(child);
 	}
 
diff --git a/common/json/json.h b/common/json/json.h
index 5167955..8b63b3b 100644
--- a/common/json/json.h
+++ b/common/json/json.h
@@ -111,7 +111,7 @@ public:
 	bool set_value(const char* key, bool val);
 	bool set_value(const char* key, int val);
 	bool set_value(const char* key, double val);
-	bool set_value(const char* key, std::string val);
+	bool set_value(const char* key, const char* val);
 	bool set_value(const char* key, json* val);
 
 	// operator+= only for array