Fix various compatibility issues with PHP 8

app/User/Avatar/LetterAvatarProvider.php

@@ -113,7 +113,7 @@ class LetterAvatarProvider extends Base implements AvatarProviderInterface
      *
      * @access protected
      * @param  string $str
-     * @return int[]
+     * @return array
      */
     protected function getHSL($str)
     {

app/User/DatabaseUserProvider.php

@@ -46,7 +46,7 @@ class DatabaseUserProvider implements UserProviderInterface
      * Get internal id
      *
      * @access public
-     * @return string
+     * @return integer
      */
     public function getInternalId()
     {

app/User/LdapUserProvider.php

@@ -117,11 +117,11 @@ class LdapUserProvider implements UserProviderInterface
      * Get internal id
      *
      * @access public
-     * @return string
+     * @return integer
      */
     public function getInternalId()
     {
-        return '';
+        return 0;
     }
 
     /**

app/User/OAuthUserProvider.php

@@ -46,11 +46,11 @@ abstract class OAuthUserProvider implements UserProviderInterface
      * Get internal id
      *
      * @access public
-     * @return string
+     * @return integer
      */
     public function getInternalId()
     {
-        return '';
+        return 0;
     }
 
     /**

app/User/ReverseProxyUserProvider.php

@@ -66,11 +66,11 @@ class ReverseProxyUserProvider implements UserProviderInterface
      * Get internal id
      *
      * @access public
-     * @return string
+     * @return integer
      */
     public function getInternalId()
     {
-        return '';
+        return 0;
     }
 
     /**