Struct contents reference from a non-struct array object

I have struct of arrays. When any struct is empty while concatenating, the above error is displayed.

d=[s1.a.d;s2.b.d;s3.c.d]

when struct a,b,c is empty above error is shown. How to redefine stacking to eliminate the error. I have also tried isstruct and isempty, but these commands are not working as expected.