Interpreter crash with function name reference

With this code

f(x) = 2*x
print(f)

both texts script and texts session crash with this error:

Traceback (most recent call last):
  File "vre-language/src/virtmat/language/utilities/errors.py", line 278, in wrapper
    return func(*args, **kwargs)
  File "vre-language/src/virtmat/language/cli/run_model.py", line 67, in run_instant_deferred
    return meta.model_from_file(clargs.model_file, deferred_mode=deferred,
  File "python-3.10.12/lib/python3.10/site-packages/textx/metamodel.py", line 715, in model_from_file
    return self.internal_model_from_file(
  File "python-3.10.12/lib/python3.10/site-packages/textx/metamodel.py", line 771, in internal_model_from_file
    model = self._parser_blueprint.clone().get_model_from_str(
  File "python-3.10.12/lib/python3.10/site-packages/textx/model.py", line 406, in get_model_from_str
    model = parse_tree_to_objgraph(
  File "python-3.10.12/lib/python3.10/site-packages/textx/model.py", line 964, in parse_tree_to_objgraph
    call_obj_processors(m._tx_metamodel, m)
  File "python-3.10.12/lib/python3.10/site-packages/textx/model.py", line 808, in call_obj_processors
    result = call_obj_processors(
  File "python-3.10.12/lib/python3.10/site-packages/textx/model.py", line 808, in call_obj_processors
    result = call_obj_processors(
  File "python-3.10.12/lib/python3.10/site-packages/textx/model.py", line 814, in call_obj_processors
    result = call_obj_processors(metamodel, attr, metaattr.cls)
  File "python-3.10.12/lib/python3.10/site-packages/textx/model.py", line 824, in call_obj_processors
    return_value_current = metamodel.process(
  File "python-3.10.12/lib/python3.10/site-packages/textx/metamodel.py", line 566, in process
    return self._obj_processors.get(_type, lambda x: x)(value)
  File "vre-language/src/virtmat/language/metamodel/processors.py", line 70, in general_reference_processor
    assert isinstance_m(obj.ref, classes)
AssertionError

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

Traceback (most recent call last):
  File "python-3.10.12/bin/texts", line 8, in <module>
    sys.exit(texts())
  File "vre-language/src/virtmat/language/cli/__init__.py", line 25, in texts
    clargs.func(clargs)
  File "vre-language/src/virtmat/language/cli/run_model.py", line 122, in main
    prog = run_instant_deferred(clargs, deferred=False)
  File "vre-language/src/virtmat/language/utilities/errors.py", line 304, in wrapper
    raise RuntimeError('non-handled exception') from err
RuntimeError: non-handled exception

The same happens if the function is used like a = f, a = 2*f etc. There should be syntax error or at least some constraints must be applied and the error should be domain-specific.