title: mongoose find() document with two fields with one search parameter
body: <p>My node model contains following properties </p>
  
  <pre><code>firstName
  lastName
  age
  address
  </code></pre>
  
  <p>I need to use mongoose find functions to filter user with firstName and lastName.</p>
  
  <p>My UI pass only one search parameter. Data should filter as follows</p>
  
  <p>'fistName' like 'search parameter' &amp; lastName like 'search Parameter'. </p>
  
  <p>I pass following object to find function.It did not work for me. </p>
  
  <pre><code>var criteria = {
      'firstName' : req.body.customerName ? { $regex: req.body.customerName, $options: 'i' } : null ,
      'lastName' : req.body.customerName ? { $regex: req.body.customerName, $options: 'i' } : null 
  };
  </code></pre>