title: Where is using null BSTR documented?
body: <p>It's at least common practice to treat null BSTR (null WCHAR* pointer) as an empty string and design all the code manipulating BSTRs accordingly. Answers to <a href="https://stackoverflow.com/questions/171641/should-there-be-a-difference-between-an-empty-bstr-and-a-null-bstr">this question</a> say the same.</p>
  
  <p>Where is this practice documented? Is there any official document describing this convention?</p>