C++ std::unique_ptr return from function and test for null

Either of the following should work:

return std::unique_ptr<myClass>{};
return std::unique_ptr<myClass>(nullptr);

To test whether the returned object points to a valid object or not, simply use:

if ( returnedData )
{
   // ...
}

See http://en.cppreference.com/w/cpp/memory/unique_ptr/operator_bool.