Lennard-Jones does not work when parameter list empty

Script:

calc = Calculator lj ()
struct = Structure ((atoms: ((symbols: 'H'), (x: 1.) [bohr], (y: 2.) [bohr], (z: 3.) [bohr])))
prop = Property energy ((calculator: calc), (structure: struct))
print(prop.energy)

Command: texts script -f script.vm

Output:

Traceback (most recent call last):
  File "jupyter-tensorflow-2023-10-10/bin/texts", line 8, in <module>
    sys.exit(texts())
  File "vre-language/src/virtmat/language/cli/__init__.py", line 28, in texts
    clargs.func(clargs)
  File "vre-language/src/virtmat/language/cli/run_model.py", line 156, in main
    evaluate_prog(prog)
  File "vre-language/src/virtmat/language/utilities/errors.py", line 307, in wrapper
    process_error(err)
  File "vre-language/src/virtmat/language/utilities/errors.py", line 295, in process_error
    raise err.__cause__
  File "vre-language/src/virtmat/language/utilities/errors.py", line 208, in wrapper
    return func(*args, **kwargs)
  File "vre-language/src/virtmat/language/utilities/typemap.py", line 117, in wrapper
    return checktype_(func(obj), obj.type_)
  File "vre-language/src/virtmat/language/interpreter/instant_executor.py", line 54, in program_value
    vals = [p.value for p in get_children_of_type('Print', self) if p.value]
  File "vre-language/src/virtmat/language/interpreter/instant_executor.py", line 54, in <listcomp>
    vals = [p.value for p in get_children_of_type('Print', self) if p.value]
  File "vre-language/src/virtmat/language/utilities/errors.py", line 307, in wrapper
    process_error(err)
  File "vre-language/src/virtmat/language/utilities/errors.py", line 295, in process_error
    raise err.__cause__
  File "vre-language/src/virtmat/language/utilities/errors.py", line 208, in wrapper
    return func(*args, **kwargs)
  File "vre-language/src/virtmat/language/utilities/typemap.py", line 117, in wrapper
    return checktype_(func(obj), obj.type_)
  File "vre-language/src/virtmat/language/interpreter/instant_executor.py", line 559, in amml_property_value
    return amml.Property(self.names, self.struct.value,
  File "vre-language/src/virtmat/language/utilities/amml.py", line 502, in __init__
    self.results = results if results is not None else self.get_results()
  File "vre-language/src/virtmat/language/utilities/amml.py", line 625, in get_results
    df['calc'] = df.apply(lambda x: apply_func(x, apply_calc), axis=1)
  File "/opt/bwhpc/common/jupyter/tensorflow/2023-10-10/lib/python3.9/site-packages/pandas/core/frame.py", line 10037, in apply
    return op.apply().__finalize__(self, method="apply")
  File "/opt/bwhpc/common/jupyter/tensorflow/2023-10-10/lib/python3.9/site-packages/pandas/core/apply.py", line 837, in apply
    return self.apply_standard()
  File "/opt/bwhpc/common/jupyter/tensorflow/2023-10-10/lib/python3.9/site-packages/pandas/core/apply.py", line 963, in apply_standard
    results, res_index = self.apply_series_generator()
  File "/opt/bwhpc/common/jupyter/tensorflow/2023-10-10/lib/python3.9/site-packages/pandas/core/apply.py", line 979, in apply_series_generator
    results[i] = self.func(v, *self.args, **self.kwargs)
  File "vre-language/src/virtmat/language/utilities/amml.py", line 625, in <lambda>
    df['calc'] = df.apply(lambda x: apply_func(x, apply_calc), axis=1)
  File "vre-language/src/virtmat/language/utilities/amml.py", line 604, in apply_func
    return func(df.structure, df.calculator, df.algorithm)
  File "vre-language/src/virtmat/language/utilities/amml.py", line 601, in apply_calc
    return calc.run(struct, constrs=constrs, properties=self.names)
  File "vre-language/src/virtmat/language/utilities/amml.py", line 387, in run
    calc_ase = self.to_ase()[0]
  File "vre-language/src/virtmat/language/utilities/amml.py", line 370, in to_ase
    calc_list.append(calc_class(**get_params_magnitudes(calc_params, self.name)))
  File "jupyter-tensorflow-2023-10-10/lib64/python3.9/site-packages/ase/calculators/lj.py", line 160, in __init__
    self.parameters.rc = 3 * self.parameters.sigma
TypeError: unsupported operand type(s) for *: 'int' and 'NoneType'