What is the difference in how you assign these node parameters? (C++)

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I have a node and I want assign 2 parameters from the Parameter Server. They are both strings:

nh.param("robot_frame", robotFrame, std::string("/base_link"));
nh.param<std::string>("world_frame", worldFrame, "/map");

When I compile, everything is OK. What I'm curious about is what is the underlying difference on how these 2 parameters are assigned? Or there is no difference at all?

Thanks!