How to resolved Warning htmlspecialchars(): charset UTF–7‘ not supported

Well, I just recently received this warning message on one of my administrators ' WordPress sites. This error occurred after the latest version of the WP website was updated.

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    Warning: htmlspecialchars(): charset UTF–7‘ not supported, assuming utf–8 in 2./home/bookis/public_html/wp–includes/formatting.php on line 3058 

Problem

htmlspecialchars() is a PHP String function which converts special characters to HTML entities.So once a special character encounters it converts it to HTML entities.

for example:

‘&’ (ampersand) becomes ‘&’

WordPress default charset it utf-8. During updating WordPress or theme etc sometimes the charset changes to UTF-7.
You Can see the changed charset in WP admin Dashboard in Settings => Reading.

It will be something like this-

Solution

The solution of the problem is that change character encoding to UTF-8 above and Refresh the site. The error should be resolved.