Object normal map does not appear correctly

Thank you Steve! So basically I don’t have to worry about it. I’m just curious why others’ don’t look like that. The normal map is filled with the blue background when it’s done baking though.
However, I just want ask you something more, when I plug in my normal map to my object (A rock), there is a obvious seam on my rock, is there anyway I can get rid of it? Or is it because I create the normal map in a wrong way?
Here are the screenshot: