How to use the scons.scons-local-250.SCons.Action._null function in SCons

    def __call__(self, target, source, env, exitstatfunc=_null, presub=_null,
                 show=_null, execute=_null, chdir=_null, executor=None):
        if executor:
            target = executor.get_all_targets()
            source = executor.get_all_sources()
        for act in self.list:
            stat = act(target, source, env, exitstatfunc, presub,
                       show, execute, chdir, executor)
            if stat:
                return stat
        return 0

kw['varlist'] = tuple(v)
    if args:
        # turn positional args into equivalent keywords
        cmdstrfunc = args[0]
        if cmdstrfunc is None or is_String(cmdstrfunc):
            kw['cmdstr'] = cmdstrfunc
        elif callable(cmdstrfunc):
            kw['strfunction'] = cmdstrfunc
        else:
            raise SCons.Errors.UserError(
                'Invalid command display variable type. '
                'You must either pass a string or a callback which '
                'accepts (target, source, env) as parameters.')
        if len(args) > 1:
            kw['varlist'] = tuple(SCons.Util.flatten(args[1:])) + kw['varlist']
    if kw.get('strfunction', _null) is not _null \
                      and kw.get('cmdstr', _null) is not _null:
        raise SCons.Errors.UserError(
            'Cannot have both strfunction and cmdstr args to Action()')

    def __call__(self, target, source, env, exitstatfunc=_null, presub=_null,
                 show=_null, execute=_null, chdir=_null, executor=None):
        act = self._generate(target, source, env, 0, executor)
        if act is None:
            raise SCons.Errors.UserError("While building `%s': "
                            "Cannot deduce file extension from source files: %s"
                % (repr(list(map(str, target))), repr(list(map(str, source)))))
        return act(target, source, env, exitstatfunc, presub,
                   show, execute, chdir, executor)

def __call__(self, target, source, env, exitstatfunc=_null, presub=_null,
                 show=_null, execute=_null, chdir=_null, executor=None):
        if executor:
            target = executor.get_all_targets()
            source = executor.get_all_sources()
        for act in self.list:
            stat = act(target, source, env, exitstatfunc, presub,
                       show, execute, chdir, executor)
            if stat:
                return stat
        return 0

def __call__(self, target, source, env,
                               exitstatfunc=_null,
                               presub=_null,
                               show=_null,
                               execute=_null,
                               chdir=_null,
                               executor=None):
        if not is_List(target):
            target = [target]
        if not is_List(source):
            source = [source]

        if presub is _null:
            presub = self.presub
            if presub is _null:
                presub = print_actions_presub
        if exitstatfunc is _null: exitstatfunc = self.exitstatfunc
        if show is _null:  show = print_actions
        if execute is _null:  execute = execute_actions
        if chdir is _null: chdir = self.chdir
        save_cwd = None
        if chdir:

def __call__(self, target, source, env,
                               exitstatfunc=_null,
                               presub=_null,
                               show=_null,
                               execute=_null,
                               chdir=_null,
                               executor=None):
        if not is_List(target):
            target = [target]
        if not is_List(source):
            source = [source]

        if presub is _null:
            presub = self.presub
            if presub is _null:
                presub = print_actions_presub
        if exitstatfunc is _null: exitstatfunc = self.exitstatfunc
        if show is _null:  show = print_actions
        if execute is _null:  execute = execute_actions
        if chdir is _null: chdir = self.chdir

def __call__(self, target, source, env, exitstatfunc=_null, presub=_null,
                 show=_null, execute=_null, chdir=_null, executor=None):
        if executor:
            target = executor.get_all_targets()
            source = executor.get_all_sources()
        for act in self.list:
            stat = act(target, source, env, exitstatfunc, presub,
                       show, execute, chdir, executor)
            if stat:
                return stat
        return 0

def __call__(self, target, source, env,
                               exitstatfunc=_null,
                               presub=_null,
                               show=_null,
                               execute=_null,
                               chdir=_null,
                               executor=None):
        if not is_List(target):
            target = [target]
        if not is_List(source):
            source = [source]

        if presub is _null:
            presub = self.presub
            if presub is _null:
                presub = print_actions_presub
        if exitstatfunc is _null: exitstatfunc = self.exitstatfunc
        if show is _null:  show = print_actions

    def __call__(self, target, source, env, exitstatfunc=_null, presub=_null,
                 show=_null, execute=_null, chdir=_null, executor=None):
        if executor:
            target = executor.get_all_targets()
            source = executor.get_all_sources()
        for act in self.list:
            stat = act(target, source, env, exitstatfunc, presub,
                       show, execute, chdir, executor)
            if stat:
                return stat
        return 0

kw['varlist'] = tuple(v)
    if args:
        # turn positional args into equivalent keywords
        cmdstrfunc = args[0]
        if cmdstrfunc is None or is_String(cmdstrfunc):
            kw['cmdstr'] = cmdstrfunc
        elif callable(cmdstrfunc):
            kw['strfunction'] = cmdstrfunc
        else:
            raise SCons.Errors.UserError(
                'Invalid command display variable type. '
                'You must either pass a string or a callback which '
                'accepts (target, source, env) as parameters.')
        if len(args) > 1:
            kw['varlist'] = tuple(SCons.Util.flatten(args[1:])) + kw['varlist']
    if kw.get('strfunction', _null) is not _null \
                      and kw.get('cmdstr', _null) is not _null:
        raise SCons.Errors.UserError(
            'Cannot have both strfunction and cmdstr args to Action()')