Currently empty paragraphs are exported to HTML with one space inside. Such paragraphs are not rendered by the browser. Such paragraph should be exported to HTML with one non-breaking space (@nbsp;) inside to ensure that they are visible in the browser.

Workaround: manually add nbsp-s in all empty paragraphs:
paragraph.Inlines.AddRun("\u00a0");


Steps to reproduce:
- Create document with empty paragraphs:

                        var document = new RadFlowDocument();
                        Section section = document.Sections.AddSection();
                        section.Blocks.AddParagraph();
                        section.Blocks.AddParagraph();
                        section.Blocks.AddParagraph();
                        section.Blocks.AddParagraph().Inlines.AddRun("test");

- Export it to HTML.

- Load the HTML in a browser.

Expected: The word 'test' is preceded by 3 empty rows.

Actual: The word 'test' is on the first row.