Build error or empty all-classes.js after compile with v3.250 and 3rd party libs

[sasklacz]

I have a really basic app utilizing ExtScheduler lib. The path to sources is added to sencha.cfg:

app.classpath=${app.dir}/lib/Sch, ${app.dir}/app

and the build/refresh/compile commands work properly, but the all-classes.js file is empty because I had to use incorrect imports to have no errors in the console :

        <!-- <x-compile> -->
            <!-- <x-bootstrap> -->
                <script src="ext/ext-all.js"></script>
               <script src="app/app.js"></script>
            <!-- </x-bootstrap> -->
        <!-- </x-compile> -->

Now if I'll try any other combination, like :

        <!-- <x-compile> -->
                <script src="ext/ext-all.js"></script>
                <script src="app/app.js"></script>             
        <!-- </x-compile> -->

or

        <!-- <x-compile> -->
            <!-- <x-bootstrap> -->
                <script src="ext/ext-all.js"></script>
            <!-- </x-bootstrap> -->
            <script src="app/app.js"></script>
        <!-- </x-compile> -->

operation crashes with the following error :

[ERR] failed to find meta class definition for name DEMO.controller.EmployeeList

So what is finally the proper way of building app with 3rd party libs ? Is the symbols.js file needed or a different approach is needed ?