code: String getFormatted() {
          StringBuilder str = new StringBuilder();
          str.append(this.propertyName);
          str.append(this.valueComparator.getComparatorString());
          if (this.value != null) {
              str.append(this.value.getFormatted());
          } else {
              str.append("null");
          }
          return str.toString();
      }
docs: Gets the constraint expressed in a string. This is for use by
  {@link Link}s for the table header.
  
  @return the constraint as a {@link String}. Guaranteed not
  <code>null</code>.