code: public final FacetOptions addFacetOnPivot(Field... fields) {
  		Assert.notNull(fields, "Pivot Facets must not be null.");
  
  		for (Field field : fields) {
  			Assert.notNull(field, "Cannot facet on null field.");
  			Assert.hasText(field.getName(), "Cannot facet on field with null/empty fieldname.");
  		}
  
  		List<Field> list = Arrays.asList(fields);
  		this.facetOnPivotFields.add(new SimplePivotField(list));
  		return this;
  	}
docs: Add pivot facet on given {@link Field}s.
  
  @param fields
  @return