Error while executing the code

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hi,
Please go through my attached code. I am getting following error when I execute it.

CasADi - 2025-03-23 17:47:14 WARNING("The options ‘t0’, ‘tf’, ‘grid’ and ‘output_t0’ have been deprecated.
The same functionality is provided by providing additional input arguments to the ‘integrator’ function, in particular:

  • Call integrator(…, t0, tf, options) for a single output time, or
  • Call integrator(…, t0, grid, options) for multiple grid points.
    The legacy ‘output_t0’ option can be emulated by including or excluding ‘t0’ in ‘grid’.
    Backwards compatibility is provided in this release only.") […/casadi/core/integrator.cpp:515]
    Traceback (most recent call last):
    File “D:\PROJECTS-PERSONAL\AI_APPLIED_TO_SSBs\0.5C_18650_2.6Ah_b.py”, line 145, in
    sol = sim.solve()
    File “C:\Python\Lib\site-packages\pybamm\simulation.py”, line 426, in solve
    self.step(
    File “C:\Python\Lib\site-packages\pybamm\simulation.py”, line 488, in step
    self._solution = solver.step(
    File “C:\Python\Lib\site-packages\pybamm\solvers\base_solver.py”, line 802, in step
    solution = self._integrate(model, t_eval, ext_and_inputs)
    File “C:\Python\Lib\site-packages\pybamm\solvers\casadi_solver.py”, line 277, in _integrate
    solution.append(current_step_sol)
    AttributeError: ‘NoneType’ object has no attribute ‘append’