fixed comment issues

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

@@ -122,7 +122,7 @@ public class DeviceEventManagementServiceImpl implements DeviceEventManagementSe
             }
             return Response.ok().entity(deviceTypeEvent).build();
         } catch (AxisFault e) {
-            log.error("failed to retrieve event definitions for tenantDomain:" + tenantDomain, e);
+            log.error("Failed to retrieve event definitions for tenantDomain:" + tenantDomain, e);
             return Response.status(Response.Status.INTERNAL_SERVER_ERROR).build();
         } catch (RemoteException e) {
             log.error("Failed to connect with the remote services:" + tenantDomain, e);
@@ -180,7 +180,7 @@ public class DeviceEventManagementServiceImpl implements DeviceEventManagementSe
             }
             return Response.ok().build();
         } catch (AxisFault e) {
-            log.error("failed to create event definitions for tenantDomain:" + tenantDomain, e);
+            log.error("Failed to create event definitions for tenantDomain:" + tenantDomain, e);
             return Response.status(Response.Status.INTERNAL_SERVER_ERROR).build();
         } catch (RemoteException e) {
             log.error("Failed to connect with the remote services:" + tenantDomain, e);
@@ -267,7 +267,7 @@ public class DeviceEventManagementServiceImpl implements DeviceEventManagementSe
             }
             return Response.ok().build();
         } catch (AxisFault e) {
-            log.error("failed to delete event definitions for tenantDomain:" + tenantDomain, e);
+            log.error("Failed to delete event definitions for tenantDomain:" + tenantDomain, e);
             return Response.status(Response.Status.INTERNAL_SERVER_ERROR).build();
         } catch (RemoteException e) {
             log.error("Failed to connect with the remote services:" + tenantDomain, e);

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

@@ -655,12 +655,12 @@ public class DeviceManagementServiceImpl implements DeviceManagementService {
         try {
             if (operationRequest == null || operationRequest.getDeviceIdentifiers() == null
                     || operationRequest.getOperation() == null) {
-                String errorMessage = "Device identifier list is empty";
+                String errorMessage = "Operation cannot be empty";
                 log.error(errorMessage);
                 return Response.status(Response.Status.BAD_REQUEST).build();
             }
             if (!DeviceMgtAPIUtils.getDeviceManagementService().getAvailableDeviceTypes().contains(type)) {
-                String errorMessage = "Device identifier list is empty";
+                String errorMessage = "Device Type is invalid";
                 log.error(errorMessage);
                 return Response.status(Response.Status.BAD_REQUEST).build();
             }