code: @Override
      protected Operand createContainsExpression(final ContainsFilter filter, final boolean not) {
          if (filter == null) {
              return null;
          }
  
          final String name = filter.getAttribute().getName();
          final String value = AttributeUtil.getAsStringValue(filter.getAttribute());
          if (StringUtil.isBlank(value)) {
              return null;
          }
  
          return new Operand(Operator.CONTAINS, name, value, not);
      }
docs: {@inheritDoc}