code: public boolean apply(final MappedField mappedField, final FilterOperator operator, final Object value,
                           final List<ValidationFailure> validationFailures) {
          if (getOperator().equals(operator)) {
              validate(mappedField, value, validationFailures);
              return true;
          }
          return false;
      }
docs: Apply validation for the given operator.  If the operator does not match the operator required by the implementing class, then this
  method will return false to show validation was not applied.  If the operator is the one being validated, this method will return
  true, and any failures in validation will be added to the list of {@code validationFailures}.
  
  @param mappedField        the field being queried
  @param operator           any FilterOperator for a query
  @param value              the query value, to apply the operator to
  @param validationFailures the list to add any failures to. If validation passes or {@code appliesTo} returned false, this list will
  not change.
  @return true if validation was applied, false if this validation doesn't apply to this operator.