Unable to do `0 * der()`

[tpdsantos]

Following the issue opened by me, previously it was possible to do something like this:

@model test begin
    c = Var(start = 0.0)
    @equations begin
        0 * der(c) = 1.0 - c
    end
end

But now this error occurs:

!!! Error from ModiaMath.NonlinearEquations.KINSOL: KINSol(...) returned with a [KINSOL] error:
    The linear solver's setup function failed in an unrecoverable manner.
ModiaMath info:
lastNorm(r) = 1.0, lastNorm(rScaled*r) = 1.0.
It might be that the Jacobian is singular (= there are redundant equations).
test: time = 0.0, stepsize of implicit Euler step = 1.0e-8, scaleConstraintsAtEvents = false
x_names     = ["c"]
x_start     = [0.0]
x_fixed     = Bool[true]
x_nominal   = [1.0]
x_yScale    = [1.0]
x_rScale    = [1.0]
x           = [0.0]
derx        = [-1.49012]
residues    = [1.0]
nx          = 1
nd          = 1
nc          = 0
nw          = 0
nz          = 0
tolerance   = 0.0001
FTOL        = 0.0001

Why is this not possible now?

Thanks in advance