Let's say the key is HKEY_CLASSES_ROOT\Folder\shell, enter image description here

and i edit the value to empty

enter image description here

Then how can this registry key reset back to (value not set) state ? I tried reg add HKCR\Folder\Shell /t REG_SZ /f(without /d) but no luck.

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    What's the significance of this "value not set"? Why is it important for you to have that state? From a functional viewpoint, they're the same – Dr.Ping Dec 24 '15 at 19:07
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    None and empty string is different in programming viewpoint, and i'm not registry expert to know t is there any side effect to left it empty. The quickest and safest way is reset to how its original look like. – 林果皞 Dec 24 '15 at 21:38
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    I'm not a programmer either. Unless you know that there is a functional difference, I'd assume that there is no difference. They're both Null. – Dr.Ping Dec 24 '15 at 21:41
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    I don't know "functional difference" or not, that's why i ask. Windows is closed source, how you know the hidden functionality powered by hidden source code ? What if this empty string for this particular registry key will crash one app in future ? Null and empty string is difference stuff in coding. – 林果皞 Dec 24 '15 at 22:26

Just delete it. The default stays there with (value not set)

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