title: Mongo "Unrecognized pipeline stage name: '$filter'"
body: <p>I'm trying to execute following query in latest mongo 3.4.1 server and the 3.4.1 shell.</p>
  
  <pre><code>db.dealer.aggregate(
  [
  {$match:{salesAreaId:{$in:[ObjectId("5858d03ec5109a098c854802")]}}},
  {$lookup:{
      from:"outstanding",
      localField:"_id",
      foreignField:"dealer_id",
      as:"outstandings"
      }},
   {$filter:{
       input:"$outstandings",
       as:"outstandings",
       cond:{
           $is:{"$$outstandings.finalized":false}
           }
       }}
  ]
  )
  </code></pre>
  
  <p>But it says </p>
  
  <pre><code>Error: command failed: {
  "ok" : 0,
  "errmsg" : "Unrecognized pipeline stage name: '$filter'",
  "code" : 40324,
  "codeName" : "Location40324"
  } : aggregate failed :
  _getErrorWithCode@src/mongo/shell/utils.js:23:13
  doassert@src/mongo/shell/assert.js:13:14
  assert.commandWorked@src/mongo/shell/assert.js:266:5
  DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1215:5
  @(shell):1:1
  </code></pre>
  
  <p>According to the <a href="https://docs.mongodb.com/v3.2/reference/operator/aggregation/filter/" rel="noreferrer">documentation</a> <code>$filter</code> is supporting from v3.2 onward.
  Any help.</p>