Avoid PHP error when enabling LDAP group provider with PHP < 5.5

ChangeLog

@@ -10,6 +10,7 @@ Bug fixes:
 
 - Fix wrong constant name that cause a PHP error in project management section
 - Fix pagination in group members listing
+- Avoid PHP error when enabling LDAP group provider with PHP < 5.5
 
 Version 1.0.22
 --------------

app/Group/LdapBackendGroupProvider.php

@@ -45,7 +45,7 @@ class LdapBackendGroupProvider extends Base implements GroupBackendProviderInter
      */
     public function getLdapGroupPattern($input)
     {
-        if (empty(LDAP_GROUP_FILTER)) {
+        if (LDAP_GROUP_FILTER === '') {
             throw new LogicException('LDAP group filter empty, check the parameter LDAP_GROUP_FILTER');
         }