Mail merge line spacing in address block

Win10Pro, LO 6.2.7, mail merge using CSV data source:

Everything about mail merge in Writer works as expected, EXCEPT address blocks created always show with double spacing, i.e. with a blank line between address elements in the address block, like the example below. How to get single spacing?!

Mr John Doe

999 Somewhere St

Anywhere, DC 99999

What are the paragraph styles for the lines? Do they include vertical spacing or a special line spacing?

The Writer document where the mail merge is created has only default Libre Office styles assigned to the entire document including the address blocks. Merged document pages look normal in every way except the address block double spaces the lines and merge fields inserted in the document behave normally.

Perhaps a style must be applied in the merge master file to the address block. Can anyone suggest what would the specs of that style be to prevent unwanted line breaks?

As a fool-proof text, enable View>Formatting Marks and check for the presence of empty paragraphs.