diff --git a/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/InfinispanUserSessionProvider.java b/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/InfinispanUserSessionProvider.java
index 85ace35908..a7c8c31ec4 100755
--- a/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/InfinispanUserSessionProvider.java
+++ b/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/InfinispanUserSessionProvider.java
@@ -478,9 +478,6 @@ public class InfinispanUserSessionProvider implements UserSessionProvider {
     void attachSession(UserSessionAdapter userSession, ClientSessionModel clientSession) {
         UserSessionEntity entity = userSession.getEntity();
         String clientSessionId = clientSession.getId();
-        if (entity.getClientSessions() == null) {
-            entity.setClientSessions(new HashSet<String>());
-        }
         if (!entity.getClientSessions().contains(clientSessionId)) {
             entity.getClientSessions().add(clientSessionId);
             userSession.update();
@@ -513,9 +510,6 @@ public class InfinispanUserSessionProvider implements UserSessionProvider {
         String clientSessionId = clientSession.getId();
         if (entity.getClientSessions() != null && entity.getClientSessions().contains(clientSessionId)) {
             entity.getClientSessions().remove(clientSessionId);
-            if (entity.getClientSessions().isEmpty()) {
-                entity.setClientSessions(null);
-            }
             userSession.update();
         }
     }
diff --git a/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/UserSessionAdapter.java b/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/UserSessionAdapter.java
index 446fe82505..bf1e6fd391 100755
--- a/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/UserSessionAdapter.java
+++ b/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/UserSessionAdapter.java
@@ -31,6 +31,7 @@ import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 /**
  * @author <a href="mailto:sthorger@redhat.com">Stian Thorgersen</a>
@@ -121,7 +122,13 @@ public class UserSessionAdapter implements UserSessionModel {
     @Override
     public void setNote(String name, String value) {
         if (entity.getNotes() == null) {
-            entity.setNotes(new HashMap<String, String>());
+            entity.setNotes(new ConcurrentHashMap<>());
+        }
+        if (value == null) {
+            if (entity.getNotes().containsKey(name)) {
+                removeNote(name);
+            }
+            return;
         }
         entity.getNotes().put(name, value);
         update();
diff --git a/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/entities/UserSessionEntity.java b/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/entities/UserSessionEntity.java
index 5c538fc514..538babfa4d 100755
--- a/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/entities/UserSessionEntity.java
+++ b/model/infinispan/src/main/java/org/keycloak/models/sessions/infinispan/entities/UserSessionEntity.java
@@ -21,6 +21,8 @@ import org.keycloak.models.UserSessionModel;
 
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.CopyOnWriteArraySet;
 
 /**
  * @author <a href="mailto:sthorger@redhat.com">Stian Thorgersen</a>
@@ -44,11 +46,11 @@ public class UserSessionEntity extends SessionEntity {
 
     private int lastSessionRefresh;
 
-    private Set<String> clientSessions;
+    private Set<String> clientSessions = new CopyOnWriteArraySet<>();
 
     private UserSessionModel.State state;
 
-    private Map<String, String> notes;
+    private Map<String, String> notes = new ConcurrentHashMap<>();
 
     public String getUser() {
         return user;
@@ -110,10 +112,6 @@ public class UserSessionEntity extends SessionEntity {
         return clientSessions;
     }
 
-    public void setClientSessions(Set<String> clientSessions) {
-        this.clientSessions = clientSessions;
-    }
-
     public Map<String, String> getNotes() {
         return notes;
     }