code: @Override
      synchronized PageWrapper insert(PageWrapper page) {
          Preconditions.checkArgument(this.incompleteNewPageOffset == PagePointer.NO_OFFSET, "Cannot insert new page while a new page is incomplete.");
          if (page.isNewPage()) {
              this.incompleteNewPageOffset = page.getOffset();
          }
  
          return super.insert(page);
      }
docs: Inserts a new PageWrapper into this PageCollection.
  
  @param page The PageWrapper to insert.
  @return The inserted PageWrapper.
  @throws IllegalArgumentException If this method was previously invoked with a PageWrapper having isNewPage() == true
  but complete() or remove() have not been called on that PageWrapper yet.