"turtle2" passed to lookupTransform argument target_frame does not exist.

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I try to achieve a demo where the second turtle will follow the first turtle, but when I run the demo, it occurs a problem which says that

[ERROR] [1595924738.621772185]: "turtle2" passed to lookupTransform argument target_frame does not exist.

Besides, the second turtle just stays still at the origin point of the turtlesim_node screen, insteading of following the first turtle.

I see the frame.pdf after I run the demo.launch, and the pdf shows that no tf data recieved. I hope this thing will help you answers answer my question.