I am user of odoo 15 community version. I install the email marketing module, then when I create a new mail I got "client error" as below:

While using google web developer tool to check, I find the error is as below:

If I click OK to continue, I can still see a new email template appear, but I find that there are further errors of 404:

I find that it is due to browser request pages like https://www\\.gmpeden\\.org/web_editor/font_to_img/61805/rgb\\(73,10,177\\)/rgb\\(255,255,255\\)/13\\.6364 

etc., as below enclosed in the red rectangle :

My question is:

1. Why there is the client error of "cannot read property of null"?

2.before that, there is a message:

is it related to the error just said?

2.But when I check the files, I did find boot.js in folder addons/web/static/src/js/, does the folder the error message said is somewhere else?

3.I check the url which is reported as giving 404 error (https://www.gmpeden.org/web_editor/font_to_img/61805/rgb(73,10,177)/rgb(255,255,255)/13.6364

 ), I cannot locate where it is. There is no sub-folder  font_to_img in addons/web_editor, so what is the reason it is missing, and how do I recover it?

Thank you very much for your help