how to squeeze multiple blank lines to one?

[GottaRun]

I have documents with one or more blank lines scattered.
How do I squeeze it to a only one blank line?

Thank you very much for the assist.

[ben_josephs]

Do you mean you want each run of consecutive blank lines reduced to a single blank line?

If the blank lines are empty,

Find what: \n\n\n
Replace with: \n\n

[X] Regular expression

Replace All -- do this repeatedly until it beeps

If the blank lines may contain spaces and tabs, you have to use

Find what: \n[ \t]*\n[ \t]*\n

[GottaRun]

cool. thank you.