FOSI has ways of detecting empty elements, as described in the attached PDF file from my book. It occurs to me now that a FOSI could write an external ASCII file (.exp file) with information about empty elements. For example:
.exp file chapter 2 title on preview page 12 has no content chapter 5 title onpreviewpage 33 has no content
With this information, you could go to the Preview page and use Synchronize Editor Position to locate the empty element in the Edit window. The following code outputs "EMPTY TITLE" to make it easy to spot.