title: What is a proper use-case of `std::nullptr_t` template parameters?
body: <p>Today I came to know that C++ allows non-type template parameters of type <code>std::nullptr_t</code>:</p>
  
  <pre><code>template&lt;std::nullptr_t N&gt; struct A { };
  
  template&lt;std::nullptr_t N&gt; void f() { } 
  </code></pre>
  
  <p>For the life of me, I cannot come up with any sensible use-case for these. Can anyone please come up with a rationale for this?</p>