Fix HTTP Error 500 issue on the role edit page

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

@@ -253,21 +253,35 @@ public class RoleManagementServiceImpl implements RoleManagementService {
             roleInfo.setPermissionList(rolePermissions);
             String[] permListAr = new String[permList.size()];
             roleInfo.setPermissions(permList.toArray(permListAr));
-
             return Response.status(Response.Status.OK).entity(roleInfo).build();
-        } catch (UserStoreException | UserAdminException e) {
-            String msg = "Error occurred while retrieving the user role '" + roleName + "'";
+        } catch (UserAdminException e) {
+            String msg = "Error occurred due to Unable to retrieve user role'" + roleName + "'";
             log.error(msg, e);
-            return Response.serverError().entity(
-                    new ErrorResponse.ErrorResponseBuilder().setMessage(msg).build()).build();
+            return Response.serverError()
+                    .entity(new ErrorResponse.ErrorResponseBuilder().setMessage(msg).build())
+                    .build();
+        } catch (UserStoreException e) {
+            String msg = "Error occurred while retrieving the UserStoreManager of the user role '"
+                    + roleName + "'";
+            log.error(msg, e);
+            return Response.serverError()
+                    .entity(new ErrorResponse.ErrorResponseBuilder().setMessage(msg).build())
+                    .build();
         }
     }
 
     private List<String> iteratePermissions(UIPermissionNode uiPermissionNode, List<String> list) {
+        //To prevent NullPointer exceptions
+        if (uiPermissionNode == null) {
+            return list;
+        }
         for (UIPermissionNode permissionNode : uiPermissionNode.getNodeList()) {
-            list.add(permissionNode.getResourcePath());
-            if (permissionNode.getNodeList() != null && permissionNode.getNodeList().length > 0) {
-                iteratePermissions(permissionNode, list);
+            if (permissionNode != null) {
+                list.add(permissionNode.getResourcePath());
+                if (permissionNode.getNodeList() != null
+                        && permissionNode.getNodeList().length > 0) {
+                    iteratePermissions(permissionNode, list);
+                }
             }
         }
         return list;