title: excluding from $match if data is blank or null in mongodb
body: <p>I am getting trouble in <code>$match</code> in <code>mongodb</code>.</p>
  
  <p>Lets say I have multiple <code>$match</code> options in some case some options are <code>blank</code> or <code>null</code> at that stage I want to <code>$match</code> do match that field in our document.</p>
  
  <p>For Example</p>
  
  <pre><code>$match:{
     name:'abc',
     age:''  //exclude if blank or null,
     city:'delhi'
  }
  </code></pre>
  
  <p>I want it only match <code>name</code> and <code>city</code> field.  I want it exclude auto if <code>blank</code> or <code>null</code> possible from aggregation.</p>