code: @Override
      protected Filter buildFilter(final String filterString, final FilteringMode filteringMode) {
          if (filterStringIsNotChanged(filterString)) {
              return null;
          }
  
          final Filter filter = super.buildFilter(filterString, filteringMode);
  
          refreshContainerIfFilterStringBecomesEmpty(filterString);
  
          lastFilterString = filterString;
          return filter;
      }
docs: Overriden not to update the filter when the filterstring (value of
  combobox input) was not changed. Otherwise, it would lead to additional
  database requests during combobox page change while scrolling instead of
  retreiving items from container cache.
  
  @param filterString
  value of combobox input
  @param filteringMode
  the filtering mode (starts_with, contains)
  @return SimpleStringFilter to transfer filterstring in container