A system security document I was editing had blank table of contents entries in Word. This was in Word 2010, but my research indicated it can happen in Word 2007, 2003, and very possibly earlier versions as well.
Since the table of contents is often the first impression of the document, you want to get it right. Many readers will assume that if the table of contents has errors, the rest of the document will too. They may be wrong, but you may not get a chance to prove it.
The particular document I was looking at had two blank entries in the table of contents. When I clicked on the links, they led to the entries right below them in the TOC, making them completely extraneous.
To eliminate these phantom whitespace entries, I went to the heading that the blank entries led to. I inserted two blank lines before and after the heading. I then copied the heading to the line above it, then deleted the old heading. Finally, I deleted the remaining blank lines.
I then returned to the table of contents, right-clicked, hit “Update Field,” and the table of contents updated properly.