code: public DayPartitionBuilder addExclusion(PlainDate date) {
  
          if (date == null) {
              throw new NullPointerException("Missing exclusion date.");
          }
  
          this.exclusions.add(date);
          return this;
  
      }
docs: /*[deutsch]
  <p>F&uuml;gt ein Ausschlu&szlig;datum hinzu. </p>
  
  @param   date    the calendar date to be excluded from creating day partitions
  @return  this instance for method chaining
  @see     DayPartitionRule#isExcluded(PlainDate)
  @see     #addExclusion(Collection)