diff --git a/imixs-workflow-core/src/main/java/org/imixs/workflow/ModelManager.java b/imixs-workflow-core/src/main/java/org/imixs/workflow/ModelManager.java
index 6a6b0ded1..cecbbdbfd 100644
--- a/imixs-workflow-core/src/main/java/org/imixs/workflow/ModelManager.java
+++ b/imixs-workflow-core/src/main/java/org/imixs/workflow/ModelManager.java
@@ -911,6 +911,9 @@ private ItemCollection lookupDefinition(final BPMNModel model) {
      * @return
      */
     private Activity lookupTaskElementByID(final BPMNModel model, int taskID) {
+        if (model == null) {
+            return null;
+        }
         Set<Activity> activities = model.findAllActivities();
         // filter the imixs activity with the corresponding id
         for (Activity activity : activities) {
diff --git a/imixs-workflow-core/src/main/java/org/imixs/workflow/bpmn/BPMNUtil.java b/imixs-workflow-core/src/main/java/org/imixs/workflow/bpmn/BPMNUtil.java
index 97e0155ac..4eb99dcca 100644
--- a/imixs-workflow-core/src/main/java/org/imixs/workflow/bpmn/BPMNUtil.java
+++ b/imixs-workflow-core/src/main/java/org/imixs/workflow/bpmn/BPMNUtil.java
@@ -121,10 +121,12 @@ private BPMNUtil() {
      * @return
      */
     public static String getVersion(BPMNModel model) {
-        List<String> valueList = getItemValueList(model, model.getDefinitions(), "txtworkflowmodelversion",
-                null);
-        if (valueList != null && valueList.size() > 0) {
-            return valueList.get(0);
+        if (model != null) {
+            List<String> valueList = getItemValueList(model, model.getDefinitions(), "txtworkflowmodelversion",
+                    null);
+            if (valueList != null && valueList.size() > 0) {
+                return valueList.get(0);
+            }
         }
         return null;
     }
diff --git a/imixs-workflow-engine/src/main/java/org/imixs/workflow/engine/WorkflowScheduler.java b/imixs-workflow-engine/src/main/java/org/imixs/workflow/engine/WorkflowScheduler.java
index 42d002572..9e91eded1 100644
--- a/imixs-workflow-engine/src/main/java/org/imixs/workflow/engine/WorkflowScheduler.java
+++ b/imixs-workflow-engine/src/main/java/org/imixs/workflow/engine/WorkflowScheduler.java
@@ -373,22 +373,22 @@ public ItemCollection run(ItemCollection configItemCollection) throws SchedulerE
                 // processWorkListByEvent(version, taskID, EventID, Group)
 
                 BPMNModel model = modelService.getModelManager().getModel(version);
-
-                // find all tasks
-                Set<Activity> activities = model.findAllActivities();
-                for (Activity task : activities) {
-                    if (BPMNUtil.isImixsTaskElement(task)) {
-
-                        ItemCollection taskEntity = BPMNEntityBuilder.build(task);
-                        int taskID = taskEntity.getItemValueInteger(BPMNUtil.TASK_ITEM_TASKID);
-                        // iterate through all scheduled events
-                        List<ItemCollection> events = modelService.getModelManager().findEventsByTask(model,
-                                taskID);
-                        for (ItemCollection eventEntity : events) {
-                            // test if this is a scheduled event...
-                            if (eventEntity.getItemValueBoolean(BPMNUtil.EVENT_ITEM_TIMER_ACTIVE)) {
-                                // eventID = eventEntity.getItemValueInteger(BPMNUtil.EVENT_ITEM_EVENTID);
-                                processWorkListByEvent(model, taskEntity, eventEntity, configItemCollection);
+                if (model != null) {
+                    // find all tasks
+                    Set<Activity> activities = model.findAllActivities();
+                    for (Activity task : activities) {
+                        if (BPMNUtil.isImixsTaskElement(task)) {
+                            ItemCollection taskEntity = BPMNEntityBuilder.build(task);
+                            int taskID = taskEntity.getItemValueInteger(BPMNUtil.TASK_ITEM_TASKID);
+                            // iterate through all scheduled events
+                            List<ItemCollection> events = modelService.getModelManager().findEventsByTask(model,
+                                    taskID);
+                            for (ItemCollection eventEntity : events) {
+                                // test if this is a scheduled event...
+                                if (eventEntity.getItemValueBoolean(BPMNUtil.EVENT_ITEM_TIMER_ACTIVE)) {
+                                    // eventID = eventEntity.getItemValueInteger(BPMNUtil.EVENT_ITEM_EVENTID);
+                                    processWorkListByEvent(model, taskEntity, eventEntity, configItemCollection);
+                                }
                             }
                         }
                     }
diff --git a/imixs-workflow-jax-rs/src/main/java/org/imixs/workflow/jaxrs/ModelRestService.java b/imixs-workflow-jax-rs/src/main/java/org/imixs/workflow/jaxrs/ModelRestService.java
index 58720a08d..52b140944 100644
--- a/imixs-workflow-jax-rs/src/main/java/org/imixs/workflow/jaxrs/ModelRestService.java
+++ b/imixs-workflow-jax-rs/src/main/java/org/imixs/workflow/jaxrs/ModelRestService.java
@@ -180,7 +180,7 @@ public String getModelXML() {
         StringBuffer sb = new StringBuffer();
         sb.append("<model>");
         try {
-            col = modelService.getVersions();
+            col = modelService.getModelManager().getVersions();
 
             for (String aversion : col) {
                 sb.append("<version>" + aversion + "</version>");
@@ -200,7 +200,7 @@ public Response findAllTasks(@PathParam("version") String version, @QueryParam("
 
         try {
             BPMNModel model;
-            model = modelService.getModel(version);
+            model = modelService.getModelManager().getModel(version);
 
             // find all tasks
             Set<Activity> activities = model.findAllActivities();
@@ -229,7 +229,7 @@ public Response findAllTasks(@PathParam("version") String version, @QueryParam("
     public Response getModelFile(@PathParam("version") String version, @Context UriInfo uriInfo) {
         try {
             // lookup model
-            BPMNModel model = modelService.getModel(version);
+            BPMNModel model = modelService.getModelManager().getModel(version);
             if (model != null) {
                 StreamingOutput stream = output -> {
                     try {
@@ -328,7 +328,7 @@ public Response findTasksByGroup(@PathParam("version") String version, @PathPara
             @QueryParam("items") String items, @QueryParam("format") String format) {
         List<ItemCollection> result = new ArrayList<>();
         try {
-            BPMNModel model = modelService.getModel(version);
+            BPMNModel model = modelService.getModelManager().getModel(version);
             BPMNProcess process = model.findProcessByName(group);
             process.init();
             Set<Activity> tasks = process.getActivities();
@@ -442,7 +442,7 @@ public void putModelByVersion(@PathParam("version") final String _modelVersion,
 
                 // delete old model if a modelversion is available
                 if (!"".equals(sModelVersion))
-                    modelService.removeModel(sModelVersion);
+                    modelService.getModelManager().removeModel(sModelVersion);
 
                 // save new entities into database and update modelversion.....
                 for (int i = 0; i < ecol.getDocument().length; i++) {
@@ -515,7 +515,7 @@ public void postModel(XMLDataCollection ecol) {
      * @throws ModelException
      */
     private String modelVersionTableToString(String rootContext) throws ModelException {
-        List<String> modelVersionList = modelService.getVersions();
+        List<String> modelVersionList = modelService.getModelManager().getVersions();
         StringBuffer buffer = new StringBuffer();
 
         for (String modelVersion : modelVersionList) {