title: How do I check whether a field contains null value? - pymongo
body: <p>Sometimes my document has a field that has null values.</p>
  
  <ul>
  <li><strong>How do I check whether the value inside a field is a null string?</strong> </li>
  <li><strong>How do I iterate through all documents and delete the field of the
  document if it has a null string value?</strong> </li>
  <li><strong>Should I delete this field for this document, so that i can do this to find the empty field?</strong> 
  <code>for i in v7.find({"eng":{"$exist":True}})</code></li>
  </ul>
  
  <p>An example of my document structure is as such:</p>
  
  <pre><code>{ "_id" : ObjectId("50fd55c1161747668078fed6"), 
  "dan" : "Hr. Hänsch repræsenterede Dem dér .", 
  "deu" : "Der Kollege Hänsch hat Sie dort vertreten .", 
  "eng" : "Mr Hänsch represented you on this occasion .", 
  "fin" : "Kollega Hänsch edusti teitä siellä .", 
  "ita" : "Il collega Hänsch è intervenuto in sua vece .", 
  "md5" : "336b9cd1dc01ae0ff3344072d8db0295", 
  "uid" : 2100986 }
  
  {u'uid': 104, 
  u'fre': u"Je crois que la pr\xe9vention est d' une importance capitale , et ce non pas \xe0 cause des criminels \xe0 la t\xeate du pouvoir .", 
  u'eng': u'', 
  u'dan': u'Som hr .', 
  u'deu': u'.', 
  u'ita': u"L' emendamento n .", 
  u'nld': u'Dat gebied is de Balkan van de toekomst , een Balkan op wereldschaal .', 
  u'spa': u'\xa1 Y no por los criminales que se hallan al frente de las instituciones !', 
  u'_id': ObjectId('50fd381f161747668058f043'), 
  u'fin': 
  u'.', u'md5': u'd41d8cd98f00b204e9800998ecf8427e'}
  </code></pre>