code: public void addFilter(String field, String valueToFilter){
          if(StringUtils.isEmpty(field) || StringUtils.isEmpty(valueToFilter)){
              throw new IllegalArgumentException("Expected all attributes to be non empty");
          }
          Set<String> valuesToFilter = new HashSet<String>();
          valuesToFilter.add(valueToFilter);
          filterQueries.put(field, new FilterFieldValue(field, valuesToFilter));
      }
docs: add a filter to the to build FilterQuery instance
  @param field
  @param valueToFilter