code: private ArrayList/*<Filter>*/ lookupFilters(String filterExpression) {
          assert filterExpression != null;
          assert !filterExpression.equals("");
  
          /* todo: perf.  caching or abstraction to make this faster */
          ArrayList/*<Filter>*/ filters = new ArrayList/*<Filter>*/();
          for(int i = 0; i < _filters.size(); i++) {
              assert _filters.get(i) instanceof Filter;
              Filter filter = (Filter)_filters.get(i);
              if(filter.getFilterExpression().equals(filterExpression))
                  filters.add(filter);
          }
  
          return filters.size() > 0 ? filters : null;
      }
docs: Internal method used to lookup {@link Filter} instances by <code>filterExpression</code>.
  @param filterExpression the filter expression whose filters to find
  @return <code>null</code> if no matching {@link Filter} objects are found; a {@link List} of {@link Filter}
  objects otherwise.