Try using:
View::yieldContent('named_section')
How does it work?
@if(View::yieldContent('named_section') !== "") @yield('named_section') @else Display my default content. @endif
If needed, you can use php functions together with yieldContent. Try passing yieldContent as a parameter to trim().
@if(trim(View::yieldContent('named_section')) !== "") @yield('named_section') @else Display my default content. @endif