Integrate a constant over an overlapped non matching meshes

Hi,

suppose I want to integrate a constant k over an overlap region of two non - matching meshes A and B - a naive approach doesn't work:

# create multimesh object
mmesh = MultiMesh()
mmesh.add(mesh_A)
mmesh.add(mesh_B)
mmesh.build()
# Create a constant k with value 1 
k = Constant(1)
# compute integral
L = k * dO
vol = assemble_multimesh(L)

It yields the error:

This integral is missing an integration domain.

What is the correct way to compute such integral on overlapped region with multimesh functionality?

Thanks,

Petr