code: public PageKey withParentId(String parentId) {
          if (StringUtil.isBlank(parentId)) {
              throw new IllegalArgumentException("Parent ID cannot be empty");
          }
          return new PageKey(parentId, this.offset, this.blockSize);
      }
docs: Creates a new {@link org.modeshape.jcr.spi.federation.PageKey} instance which has the given parent ID and the same
  offset & block size as this page.
  @param parentId a {@link String} representing the ID of the new parent; may not be null.
  @return a new {@link org.modeshape.jcr.spi.federation.PageKey} instance; never null.