set the compiler arguments "swf-version"
For Flash Player 11.4 and earlier and AIR 3.4 and earlier, stack traces are only available when code is running in the debugger version of Flash Player or the AIR Debug Launcher (ADL). In non-debugger versions of those runtimes, calling this method returns null.
e.g: use flash player 11.6, the swf-version value is 19
BTW, sdk3.5 can not parse the swf-version, it's too bad.