htaccess misconfiguration 500

So basically i created a .htaccess file which removes .html extension and redirects /file.html to /file but when i write /file.html/ it causes a 500 internal server error, How can I map/file.html/ to my custom error page ? or simply redirect that also to /file.html

Here is the code :

Options -Indexes
ErrorDocument 404 /custom404.html
ErrorDocument 403 /custom404.html
ErrorDocument 500 /custom404.html


RewriteEngine on



RewriteCond %{THE_REQUEST} .html [NC]
RewriteRule ^(.*).html$ /$1 [R=301,L]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME}.html -f
RewriteRule ^(.*)$ $1.html [L]

Answer

With your shown samples, could you please try following(comments have been added in rules for explanation). Please make sure to clear your browser cache before testing your URLs.

Options -Indexes
ErrorDocument 404 /custom404.html
ErrorDocument 403 /custom404.html
ErrorDocument 500 /custom404.html

RewriteEngine on
##Added additional condition to make sure this runs from external request only.
RewriteCond %{ENV:REDIRECT_STATUS} ^$
RewriteCond %{THE_REQUEST} s/.*.htmls [NC]
RewriteRule ^(.*).html/?$ /$1 [R=301,L,NC]

##Simply rewrite from non-existing pages to html files.
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{DOCUMENT_ROOT}/$1.html -f
RewriteRule ^(.*)/?$ $1.html [L]