title: `fields cannot be identical: ' ' and ' '` mongoimport error
body: <p>i'm trying to import a csv into mongodb on my local machine.  I used the following commmand from the shell:</p>
  
  <pre><code>mongoimport -d mydb -c things --type csv --file /Users/..../agentsFullOutput.csv --headerline
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>Failed: fields cannot be identical: '' and ''
  </code></pre>
  
  <p>I can't find anything on what that means.  What am I doing wrong?  The csv file, by the way, is the result of a mongoexport.</p>
  
  <p>here are the column headers and some data:</p>
  
  <pre><code>_id build_profile   company_address company_name    company_website created_at  device _token   downloaded_app  email   first_name  last_name   is_proapp   modified_at mobile_phone    terms_accepted_at   license_number  broker_id   join_unique_url linkedin_profile_id billing_customer_id billing_zip mobile_phone    office_phone    vendors_count   clients_count   app_client
  ObjectID(52ab245b763f4aec448b6763)  0   California  Lateral test    2014-01-01T08:19:05.470Z            test    test    test        2015-04-18T05:16:37.155Z    (123) 123-1234                          zip (123) 123-1234      10  5   
  ObjectID(52b46bfc763f4ad9198b45ab)      7928    test    test    2014-01-01T08:19:05.470Z                Jennifer    Chase       2015-04-15T17:05:17.114Z            5551112     jennifer-chase      test    7071            22  64  
  </code></pre>