diff --git a/full/Changes b/full/Changes
index a5a1ddc..abfa4f0 100644
--- a/full/Changes
+++ b/full/Changes
@@ -3,6 +3,8 @@
 2022-05-12
  - Implemented mapping of LDAP username to email
  - Handled null parameters in authorization requests
+2022-05-25
+ - Fixed null client_id
 
 # version 0.67
 
diff --git a/full/src/main/java/de/ids_mannheim/korap/oauth2/oltu/service/OltuAuthorizationService.java b/full/src/main/java/de/ids_mannheim/korap/oauth2/oltu/service/OltuAuthorizationService.java
index a3b9b01..0ac3da6 100644
--- a/full/src/main/java/de/ids_mannheim/korap/oauth2/oltu/service/OltuAuthorizationService.java
+++ b/full/src/main/java/de/ids_mannheim/korap/oauth2/oltu/service/OltuAuthorizationService.java
@@ -108,7 +108,7 @@
 
     public OAuthProblemException checkRedirectUri (OAuthProblemException e,
             String clientId, String redirectUri) {
-        if (!clientId.isEmpty()) {
+        if (clientId !=null && !clientId.isEmpty()) {
             String registeredUri = null;
             try {
                 OAuth2Client client = clientService.retrieveClient(clientId);