🐛 fix leak for strings

include/nlohmann/detail/conversions/to_json.hpp

@@ -236,7 +236,10 @@ template<typename BasicJsonType, typename CompatibleString,
          enable_if_t<std::is_constructible<typename BasicJsonType::string_t, CompatibleString>::value, int> = 0>
 void to_json(BasicJsonType& j, const CompatibleString& s)
 {
-    j.m_value.destroy(j.m_type);
+    if (!j.is_null())
+    {
+        j = nullptr;
+    }
     external_constructor<value_t::string>::construct(j, s);
 }