[Stefan]

Oh, you was faster than I?
 

I have just this moment worked on this too :

//JavaScript Macro for EmEditor, v0.01 by Stefan
//Purpose: Ensure that last line is a blank one, by adding one if need.

//EmEditor Help - EmEditor Macro Reference - Document Object
//Retrieves the number of the lines in the document:
nLines = document.GetLines();

//Retrieves the text on the specified line:
str = document.GetLine(nLines);

if(str.length != 0){
//If last line is NOT empty, add one blank line:
	document.selection.EndOfDocument();
	document.selection.NewLine();
	
	//Workaround: Delete automatically added indenting from line above,// 
	//if line was not empty but indented by white space//
	//Selects a line at the cursor:
	document.selection.SelectLine();
	//Deletes the selected text:
	document.selection.Delete();	
}