title: How are Mono<Void> and Mono.empty() different
body: <p>As per my understanding, in Spring WebFlux reactor </p>
  
  <p><code>Mono&lt;Void&gt;</code> refers for a void Mono</p>
  
  <p><code>Mono.empty()</code> refers to void, as calling anything over this gives a null pointer.</p>
  
  <p><em>How do these stand different in their usage ?</em></p>