delete-trailing-lines

delete-trailing-lines is a variable defined in `simple.el'.
Its value is

t

Documentation:
If non-nil, M-x delete-trailing-whitespace deletes trailing lines.
Trailing lines are deleted only if `delete-trailing-whitespace'
is called on the entire buffer (rather than an active region).

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.3 of Emacs.