Language: PHP
Label: safe
CWE: CWE-79 \u2014 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

Code:
    function write_file(string $data, string $file_location, string $mode ="a") {

        // If error msg not empty
        if(!empty($data)) {

            $fp = fopen(DIR_BASE . $file_location, $mode); // use w for truncate /clear content
            fwrite($fp, $data);
            fclose($fp);

        }

    }