Ying/error msg

[YingXue]

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This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.

Thank you for contributing to the Azure IoT Explorer!

This checklist is used to make sure that common guidelines for a pull request are followed.

General Guidelines

• If introducing new functionality or modified behavior, are they backed by unit tests?
• Have all unit tests passed locally? (by running npm run test command)
• Have you updated the README.md with new screenshots if significant changes have been made?
• Have you update the package version if the current version in package.json is not higher than the version released?