hm, ( again play your example: G4P EditTextControls Textarea 1 )
i can type text and [enter] go next line.
[enter] again does not create ONE empty line.
[space][enter] creates a line what looks like a empty line.
if i have many lines and go up with cursor and delete the content of a line
a empty line can be created ( so it is allowed by your textarea field ).
if i try to create a second empty line this way ( deleting the content of a existing line after a empty line ) the line is removed, like you suggested.
when i am at the end of a not empty line and press [enter] a following empty line is created.
sorry @quark, i think a [enter] at the beginning of a line should be allowed ( to create ONE empty line ).
environment:
Raspbery Pi, OS RASPBIAN && win 7 / 64b
Processing 3.5.2
G4P 4.2.0