Fit report errors when Hantush function is used

[raoulcollenteur]

Describe the bug

Using the Hantush function ends up in an Error in the fit_report.

To Reproduce

ml = ps.Model(head)
sm = ps.RechargeModel(prec, evap, rfunc=ps.Hantush(), name="rch")
ml.add_stressmodel(sm)
ml.solve(report=True)

gives:

in Hantush.get_tmax(self, p, cutoff)
    870 if cutoff is None:
    871     cutoff = self.cutoff
--> 872 a, b = p[1:]
    873 rho = 2 * np.sqrt(b)
    874 return lambertw(1 / ((1 - cutoff) * k0(rho))).real * a

ValueError: too many values to unpack (expected 2)

Expected behavior

No error.

Python package version
pastas 1.5.0