[BUG]: Issue with const in `tests/classes.rn`

[Almas-Ali]

Describe the bug Throwing error while change const in this file. Not related to Radon exception.

Screenshots or Code snippets Code: tests/classes.rn file.

    static const c = "i am static const" # line:26
    c = "i am static var" # line: 27

Error:

Traceback (most recent call last):
  File "***/radon/radon.py", line 61, in <module>
    (result, error, should_exit) = base_core.run(
                                   ^^^^^^^^^^^^^^
  File "***/radon/core/builtin_funcs.py", line 527, in run
    result = interpreter.visit(ast.node, context)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "***/radon/core/interpreter.py", line 14, in visit
    return method(node, context)
           ^^^^^^^^^^^^^^^^^^^^^
  File "***/radon/core/interpreter.py", line 37, in visit_ArrayNode
    elements.append(res.register(self.visit(element_node, context)))
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "***/radon/core/interpreter.py", line 14, in visit
    return method(node, context)
           ^^^^^^^^^^^^^^^^^^^^^
  File "***/radon/core/interpreter.py", line 424, in visit_CallNode
    return_value = res.register(value_to_call.execute(args))
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "***/radon/core/builtin_funcs.py", line 42, in execute
    return_value = res.register(method(exec_ctx))
                                ^^^^^^^^^^^^^^^^
  File "***/radon/core/builtin_funcs.py", line 480, in execute_require
    f'Failed to finish executing script "{module}"\n' + error.as_string(),
                                                        ^^^^^^^^^^^^^^^^^
  File "***/radon/core/errors.py", line 101, in as_string
    result = self.generate_traceback()
             ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "***/radon/core/errors.py", line 113, in generate_traceback
    result = f"  File {pos.fn}, line {str(pos.ln + 1)}, in {ctx.display_name}\n" + result
                       ^^^^^^
AttributeError: 'NoneType' object has no attribute 'fn'

Additional context A issue with OOP.