People are often confused that they add a breakpoint on some (empty) line and
the debugger stops at another (the first non-empty) line.

It would be good if actions for adding line breakpoints (Toggle Breakpoint, Add
Breakpoint) would warn before adding a breakpoint on an empty line.

Proposal - draft:

1) Toggle Breakpoint--------------------When a user invokes action on an empty
line, a dialog appears allowing to choose between two options:

   ooo  Put the breakpoint on another line
        Line number: [xxx]

             (where 'xxx' is number of the first non-empty line below
              the current line)

   ooo  Cancel

2) Add breakpoint dialog
------------------------
When adding breakpoint via the "Add Breakpoint" dialog, the source code may not
be available.

a) The source code is available

   i) Source editor was selected at the time the "Add Breakpoint" action was
      invoked.

       The dialog contains pre-filled values for Package, Class and Line Number
       of the breakpoint. If the editor cursor was at an empty line, do not
       offer this line but the first non-empty line below it.

  ii) Source editor was not selected.

       Field "Line Number" is not pre-filled.
  In both cases, perform a check at the moment the user presses the OK button.
  If an empty (or invalid) line number is entered in the "Line Number" field,
  display a warning and offer another line number (again, the first
  non-empty...).

b) The source code is not available

  The only way how to check whether a line number is legal is to get a list
  of VM locations of a ReferenceType (see package com.sun.jdi). This is
  possible only if the debugger is running and the class (represented by an
  object of type ReferenceType) is prepared.