code: public final Filter<S> orExists(String propertyName, Filter<?> subFilter) {
          ChainedProperty<S> prop = new FilterParser<S>(mType, propertyName).parseChainedProperty();
          return or(ExistsFilter.build(prop, subFilter, false));
      }
docs: Returns a combined filter instance that accepts records which are
  accepted either by this filter or the "exists" test applied to a join.
  
  @param propertyName one-to-many join property name, which may be a chained property
  @param subFilter sub-filter to apply to join, which may be null to test
  for any existing
  @return canonical Filter instance
  @throws IllegalArgumentException if property is not found
  @since 1.2