Fixing https://github.com/wso2/product-iots/issues/447.

components/device-mgt/org.wso2.carbon.device.mgt.api/src/main/java/org/wso2/carbon/device/mgt/jaxrs/service/impl/GroupManagementServiceImpl.java

@@ -174,6 +174,9 @@ public class GroupManagementServiceImpl implements GroupManagementService {
             return Response.status(Response.Status.OK).build();
         } catch (GroupManagementException e) {
             String msg = "Error occurred while managing group share. ";
+            if (e.getErrorMessage() != null){
+                msg += e.getErrorMessage();
+            }
             log.error(msg, e);
             return Response.status(Response.Status.INTERNAL_SERVER_ERROR).entity(msg).build();
         } catch (RoleDoesNotExistException e) {

components/device-mgt/org.wso2.carbon.device.mgt.core/src/main/java/org/wso2/carbon/device/mgt/core/service/GroupManagementProviderServiceImpl.java

@@ -367,6 +367,7 @@ public class GroupManagementProviderServiceImpl implements GroupManagementProvid
     @Override
     public void manageGroupSharing(int groupId, List<String> newRoles)
             throws GroupManagementException, RoleDoesNotExistException {
+        if (newRoles != null) {
             int tenantId = CarbonContext.getThreadLocalCarbonContext().getTenantId();
             UserStoreManager userStoreManager;
             try {
@@ -401,6 +402,9 @@ public class GroupManagementProviderServiceImpl implements GroupManagementProvid
             } finally {
                 GroupManagementDAOFactory.closeConnection();
             }
+        } else {
+            throw new GroupManagementException("No roles provided to complete the operation.");
+        }
     }
 
     /**

components/device-mgt/org.wso2.carbon.device.mgt.ui/src/main/resources/jaggeryapps/devicemgt/app/pages/cdmf.page.groups/groups.hbs

@@ -381,7 +381,7 @@
                     <div class="content">
                         <div class="row">
                             <div class="col-lg-5 col-md-6 col-centered">
-                                <h3>Unexpected error occurred!</h3>
+                                <h3 id="unexp-error-msg">Unexpected error occurred!</h3>
 
                                 <div class="buttons">
                                     <a href="#" id="group-unexpected-error-link" class="btn-operations">

components/device-mgt/org.wso2.carbon.device.mgt.ui/src/main/resources/jaggeryapps/devicemgt/app/pages/cdmf.page.groups/public/js/listing.js

@@ -633,6 +633,9 @@ function displayErrors(jqXHR) {
         });
     } else {
         $(modalPopupContent).html($('#group-unexpected-error-content').html());
+        if (jqXHR.responseText) {
+            $('#unexp-error-msg').html(jqXHR.responseText.replace(new RegExp("\"", 'g'), ""));
+        }
         $("a#group-unexpected-error-link").click(function () {
             hidePopup();
         });