Eng 1123 enable operator with no return

[Boyuan-Deng]

Describe your changes and why you are making these changes

Before this implementation, is the user declared a @op for a function with null return, our system will produce a error. I wrote the code to enable operator with no return type.

Related issue number (if any)

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• [ ] If this is a new feature, I have added unit tests and integration tests.
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• [ ] All features on the UI continue to work correctly.
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