code: public static FilterBuilder buildFilter(Criteria criteria) {
          if (criteria.getTransaction() != null && criteria.getTransaction().trim().isEmpty()) {
              return FilterBuilders.missingFilter(TRANSACTION_FIELD);
          }
          return null;
      }
docs: This method returns a filter associated with the supplied criteria.
  
  @param criteria The criteria
  @return The filter, or null if not relevant