code: def find(key):
      
      docs = list(collection.find({KEY_FIELD: key}))
      # Return None if we didn't find anything.
      if not docs:
          return None
      pickled_value = docs[0][VALUE_FIELD]
      # Unpickle and return the value.
      return pickle.loads(pickled_value)
docs: Return the value associated with a key.
  
      If there is no value with the given key, returns ``None``.