title: c++ function return NULL string reference
body: <p>I have a function has a return type of <code>std::string&amp;</code> and how do I return a NULL <code>string&amp;</code> if no condition matches in the function?</p>
  
  <pre><code>std::string&amp; SomeClass::getSomething()
  {
       if(){...}
       else if(){...}
       // return a NULL
  }
  </code></pre>