Re: deleting a null pointer

Given the snippet.

class foo {
public:
  ~foo() {
    // type id should be able to get the type of the class ( I think )
    std::cout << " foo destructing " << std::endl;
  }
};

int main() {

  foo *ptr = new foo () ;
  delete ptr;

  foo *ptr_ ( 0 );
  if ( ptr_ ) {
    delete ptr_ ;
  }
}

If memory serves the check "if ( ptr_ )" is NEVER (UN) necessary.
Trouble is, I don't recall the impetus surrounding why or where in the
standard I found this. My standard is not within arms reach that
said, the question: Could I get confirmation on that deleting a void
pointer is indeed valid and where (source) in the standard I could
confirm this?