Tell me please what is different between
return null;
and
return (null);
Sometime i'd seen each an examples

There's no difference in behaviour whatsoever - but the latter is distinctly unidiomatic. I've previously seen it as a sign that the author seems to think that return is a function call, or at least want to treat it as such. (Sometimes there are brackets around every return value.)
Just use the first version.
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