title: Mongodb aggregation pipeline stages
body: <p>I have an aggregation of say 4 stages match,lookup, unwind, project as mentioned in the same order.</p>
  <p>Suppose if the resultant data from the match stage is null that is it does not return any document then does the aggregation breaks?  or it passes null data to next stage and executes all the next stages?</p>
  <p>If it executes all the next stage then how to break the aggregation when the result of match query is null.</p>
  <p>I am asking this so that i can minimise the query to the database.</p>