Mail merge in Writer wants me to provide a Java runtime environment

Once a year I need to run a small mail merge and up to now it has been fine. This year, with an upgraded version, (6.3.5.2) when I try to select the data I get a message requiring me to set a Java runtime environment through Advanced Options. I am no IT expert and have not got the slightest idea what this means. When I follow the instructions as above I arrive at a blank window which seems to require me to select something but there is nothing to select - and I don’t know what I should do. Please help.

Is there a checkmark next to “Java Options” left of Use a java runtime environment ?
If Java is enabled there, but no entry shown below, tell again here. Do not use the Add Answer for the pupose, but add a comment.

BTW: I never use Mailmerge, and cannot tell anything about it, but generally the java dependence of LibreOffice decreased over years now. I had cases where an alert to the effect “need java” popped up, but the respective feature worked flawlessly if I simply quit the alert.
And: Just did a tiny experiment with the Mailmerge wizard without java support and didn’t get an alert.
What data source did you try to select? Was it an ordinary LibreOffice document or a database table?

In addition to @Lupp:

What is Java used for in LibreOffice?

Thanks for coming back. I have decided that the list is small enough to do the job manually. Often mailmerge ends up being more trouble than it’s worth. I think that is the case here. Thank you again.