Throw workflow not found as the default behaviour for IBM, GCP and AWS

provider/workflow-aws/src/main/java/org/opengroup/osdu/workflow/aws/repository/AwsWorkflowSystemMetadataRepository.java

 package org.opengroup.osdu.workflow.aws.repository;
 
+import org.opengroup.osdu.workflow.exception.WorkflowNotFoundException;
 import org.opengroup.osdu.workflow.model.WorkflowMetadata;
 import org.opengroup.osdu.workflow.provider.interfaces.IWorkflowSystemMetadataRepository;
 import org.springframework.stereotype.Repository;
@@ -19,7 +20,7 @@ public class AwsWorkflowSystemMetadataRepository implements IWorkflowSystemMetad
    */
   @Override
   public WorkflowMetadata getSystemWorkflow(String workflowName) {
-    return null;
+    throw new WorkflowNotFoundException(String.format("Workflow: '%s' not found", workflowName));
   }
 
   /**

provider/workflow-gcp/src/main/java/org/opengroup/osdu/workflow/provider/gcp/repository/GcpWorkflowSystemMetadataRepository.java

@@ -2,6 +2,7 @@ package org.opengroup.osdu.workflow.provider.gcp.repository;
 
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
+import org.opengroup.osdu.core.common.exception.NotFoundException;
 import org.opengroup.osdu.workflow.model.WorkflowMetadata;
 import org.opengroup.osdu.workflow.provider.interfaces.IWorkflowSystemMetadataRepository;
 import org.springframework.stereotype.Service;
@@ -21,7 +22,8 @@ public class GcpWorkflowSystemMetadataRepository implements IWorkflowSystemMetad
    */
   @Override
   public WorkflowMetadata getSystemWorkflow(String workflowName) {
-    return null;
+    throw new NotFoundException(
+        String.format("Workflow entity for workflow name: %s not found.", workflowName));
   }
 
   /**

provider/workflow-ibm/src/main/java/org/opengroup/osdu/workflow/provider/ibm/repository/WorkflowSystemMetadataRepository.java

 package org.opengroup.osdu.workflow.provider.ibm.repository;
 
 import lombok.extern.slf4j.Slf4j;
+import org.apache.http.HttpStatus;
+import org.opengroup.osdu.core.common.model.http.AppException;
 import org.opengroup.osdu.workflow.model.WorkflowMetadata;
 import org.opengroup.osdu.workflow.provider.interfaces.IWorkflowSystemMetadataRepository;
 import org.springframework.stereotype.Component;
@@ -19,7 +21,7 @@ public class WorkflowSystemMetadataRepository implements IWorkflowSystemMetadata
    */
   @Override
   public WorkflowMetadata getSystemWorkflow(String workflowName) {
-    return null;
+    throw new AppException(HttpStatus.SC_NOT_FOUND, "workflow not found", String.format("Workflow: %s doesn't exist", workflowName));
   }
 
   /**