AttributeError in function with comparison expression with string parameter

f(x) = x == '1'
b = f('2')

Traceback (most recent call last):
  File "vre-language/src/virtmat/language/utilities/errors.py", line 94, in wrapper
    return func(*args, **kwargs)
  File "../scripts/run_model.py", line 54, in run_instant_deferred
    return meta.model_from_file(clargs.model_file, deferred_mode=deferred,
  File "jupyter-tensorflow-2023-01-02/lib64/python3.8/site-packages/textx/metamodel.py", line 658, in model_from_file
    return self.internal_model_from_file(
  File "jupyter-tensorflow-2023-01-02/lib64/python3.8/site-packages/textx/metamodel.py", line 712, in internal_model_from_file
    p(model, self)
  File "vre-language/src/virtmat/language/metamodel/function.py", line 42, in function_call_processor
    new_obj.parent = new_obj.parent.last_copy
AttributeError: 'Comparison' object has no attribute 'last_copy'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "../scripts/run_model.py", line 96, in <module>
    main()
  File "../scripts/run_model.py", line 86, in main
    prog = run_instant_deferred(clargs, deferred=False)
  File "vre-language/src/virtmat/language/utilities/errors.py", line 99, in wrapper
    raise RuntimeError('non-handled exception') from err
RuntimeError: non-handled exception