tf2_ros::Buffer.transform() missing timestamp

edit

Hello everyone I use tf2_ros::Buffer.transform() to transform a geometry_msgs::WrenchStamped into ageometry_msgs::WrenchStamped in another frame at the same time. So the syntax is:

tf2_ros::Buffer.transform(geometry_msgs::WrenchStamped wrenchStamped1, geometry_msgs::WrenchStamped wrenchStamped2, const std::string & target_frame, ros::Duration timDur);

It seems to work fine but the wrenchStamped2 has an empty timestamp. Is this on purpose by the function and do I need to manually assign the timestamp?

The code looks basically like this (msg is the message from the subscriber callback function this code snippet is part of):

 geometry_msgs::WrenchStamped msgWrench = msg->wrench;
 msgWrench.header = msg->header;
 msgWrench.header.frame_id = "EE_FORCETORQUESENSOR";

 geometry_msgs::WrenchStamped worldFrameWrenchFTSensorStamped;
  try 
  {
    ros::Duration timDur(0.1);
    std::string target_frame_("world");
    buffer_.transform(msgWrench, worldFrameWrenchFTSensorStamped, target_frame_, timDur);
  }
  catch (tf2::TransformException &ex) 
  {
    ROS_WARN("Failure %s\n", ex.what()); //Print exception which was caught
  }

  worldFrameWrenchFTSensorStamped.header = msgWrench.header;