Not extracting edge data when using meshToPet function with structural model

I am using the meshToPet fuction on a mesh generated from a strcuturalmodel.

structuralmodel = createpde('structural','static-solid');
L=  1; %m
W = 1; %m
aSi = 0.5; %m
cSi = 0.5; %m
gm = multicuboid(L,W,[cSi,aSi],'Zoffset',[0,cSi]);

structuralmodel.Geometry = gm
structuralBC(structuralmodel,'Face',[5,10],'Constraint','fixed');
order='linear';
generateMesh(structuralmodel,'Hmax',cSi,'GeometricOrder',order);
[p,e,t]=meshToPet(structuralmodel.Mesh);

But the meshToPet function returns a empry 'e' (FEMeshAssociation) variable. How can I get the edge data from the structural model date so that I can then insert in back in using

assoc = pde.FEMeshAssociation(t,e);
structuralmodel.Mesh = pde.FEMesh(p, t(1:4,:), Hmax, Hmin, 1.5,order,assoc);