Created attachment 86931 [details]
Screenshots illustrating the issue

AOO 4.1.7
AOO417m1(Build:9800)  -  Rev. 46059c9192
2019-09-03 12:04

Steps to reproduce:

1. Launch AOO Writer
2. Menu 'View -> Nonprinting Characters'
  (this step is not necessary but it allows to notice the problem
   immediately)
3. Invoke Find & Replace dialog
   Menu 'Edit -> Find & Replace'  OR  Control+F
   
   Both fields: 'Search for' and 'Replace with' shall be empty.

4. Place cursor in 'Search for' field.
5. Press Enter.
   AOO Writer inserts an empty line.
6. Place cursor in 'Replace with' field.
7. Press Enter.
   AOO Writer inserts an empty line.

This is not an expected result. Nothing should be inserted.

Note:
Shall the user be notified of search result?
In case of searching for "empty string" via Find toolbar, AOO displays message "Search key not found.", but icons for upward/downward search are active. In 'Find & Replace' dialog, buttons for search/replace are not active (grayed out).

In case of "empty string" in Find & Replace dialog, Basic IDE, user is not notified just as e.g. in MS Word or NotePad++


Screenshots are placed in attached file "LinesInserted".