Example test_excel not runable

The CryoGrid test case test_excel is currently not runable.
It results in the following error message:

Undefined function 'get_boundary_condition_u' for input arguments of type 'FORCING_seb'.

Error in GROUND_fcSimple_salt_seb_snow/get_boundary_condition_u (line 34)
                ground.IA_CHILD = get_boundary_condition_u(ground.IA_CHILD, forcing); %call boundary condition for child

Error in main (line 59)
    TOP.NEXT = get_boundary_condition_u(TOP.NEXT, forcing);

Attempted using MATLAB R2018b, and CryoGrid model commit 3abeea8430d5d33667f6cf87f82341f827a2f28b.

The other test case test_crocus runs without problems.