code: public static OverwritePolicy byAttributes(String firstAttribute, String... otherAttributes) {
  		List<String> attributes = new ArrayList<String>();
  		attributes.add(firstAttribute);
  		attributes.addAll(Arrays.asList(otherAttributes));
  		return new AttributeOverwritePolicy(attributes);
  	}
docs: Returns an {@link OverwritePolicy} that deletes records that are
  identical in the specified attributes with a record being imported. As a
  result, no two records can exist in the data set that have the same
  values for all of those attributes at once. <br>
  At least one attribute needs to be specified.
  <p>
  Empty attribute values in existing data are treated as matching anything.
  Existing records that match an imported record on all non-empty
  attributes are deleted.
  
  @param firstAttribute first attribute
  @param otherAttributes additional, optional attributes
  @return a policy deleting non-unique data by selected attributes