How can I hide null members in watch screen? I don’t need that.
Below is an screenshot:

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It doesn’t work that way. The inspector is there for you to see all available members. The visibility of the members never has anything to do with the value of the member, null or otherwise. Conceivably you might be able to write a plugin that replaces the inspector in its entirety, to do what you want, but that would be a lot of work.