error with empty calculator

According to grammar this statement is allowed: calc = Calculator emt (). But I get an error during type checking:

Traceback (most recent call last):
  File "vre-language/src/virtmat/language/utilities/errors.py", line 91, in wrapper
    return func(*args, **kwargs)
  File "vre-language/examples/../scripts/run_model.py", line 54, in run_instant_deferred
    return meta.model_from_file(clargs.model_file, deferred_mode=deferred,
  File "python-3.10.6/lib/python3.10/site-packages/textx/metamodel.py", line 658, in model_from_file
    return self.internal_model_from_file(
  File "python-3.10.6/lib/python3.10/site-packages/textx/metamodel.py", line 712, in internal_model_from_file
    p(model, self)
  File "vre-language/src/virtmat/language/constraints/typechecks.py", line 59, in check_types_processor
    _ = obj.type_
  File "/usr/lib/python3.10/functools.py", line 981, in __get__
    val = self.func(instance)
  File "vre-language/src/virtmat/language/constraints/typechecks.py", line 97, in variable_type
    return self.parameter.type_
  File "/usr/lib/python3.10/functools.py", line 981, in __get__
    val = self.func(instance)
  File "vre-language/src/virtmat/language/constraints/typechecks.py", line 845, in amml_calculator_type
    if isinstance_m(self.parameters, ['Table']):
  File "vre-language/src/virtmat/language/utilities/textx.py", line 17, in isinstance_m
    meta = get_metamodel(obj)
  File "python-3.10.6/lib/python3.10/site-packages/textx/model.py", line 67, in get_metamodel
    return get_model(obj)._tx_metamodel
AttributeError: 'NoneType' object has no attribute '_tx_metamodel'

Obviously default is False and parameters is None but this is no valid case. If default is False then parameters may not be None. If default is True then parameters must be None. Either the grammar must be changed to disallow these combinations or the constraints must be fixed.