What's wrong with running yolov5 (1) p, r, map are all 0

1. I encountered an embarrassing problem when running today
During training, p, r, and map are all 0

The above image may not be very intuitive
Including the final result also has no precision, recall and map.

There are many reasons for no results after inquiring (the following reasons range from easy to operate to difficult to operate records):
①The format is not converted
②There is a problem with the folder format (name and structure)
A certainSome versions seem to have metaphysical renaming operations
③The pytorch and cuda versions do not correspond

This time I made a small mistake that only a wise man would make.A point to remind: When checking, you must start from the bottom.

My root cause is: txt for train training set, xml for val

Then I think there is a point that few bloggers will mention:
yolov5 actually only uses the corresponding image files and txt folders for training.In fact, as long as you have these two, it will be fine!!!