# Buggy code
def _validate_internal_indices(self, mode=None, **kwargs):
    """
    Validates and optionally updates internal and external indices
    of modin_frame in specified mode. There is 3 modes supported:
        1. "reduced" - validates and updates indices on that axes
            where external indices is ["__reduced__"]
        2. "all" - validates indices at all axes, optionally updates
            internal indices if `update` parameter specified in kwargs
        3. "custom" - validation follows arguments specified in kwargs.

    Parameters
    ----------
        mode : str or bool, default None
        validate_index : bool, (optional, could be specified via `mode`)
        validate_columns : bool, (optional, could be specified via `mode`)
    """

    if isinstance(mode, bool):
        mode = "all"

    reduced_sample = pandas.Index(["__reduced__"])
    args_dict = {
        "custom": kwargs,
        "reduced": {
            "validate_index": self.index.equals(reduced_sample),
            "validate_columns": self.columns.equals(reduced_sample),
        },
        "all": {"validate_index": True, "validate_columns": True},
    }

    args = args_dict.get(mode, args_dict["custom"])

    if args.get("validate_index", True):
        self._validate_axis_equality(axis=0)
    if args.get("validate_columns", True):
        self._validate_axis_equality(axis=1)


# Traceback (Exception)
FutureWarning: pandas.core.index is deprecated and will be removed in a future version.  The public classes are available in the top-level namespace.
UserWarning: User-defined function verification is still under development in Modin. The function provided is not verified.
empty !
Traceback (most recent call last):
File "./test2.py", line 24, in <module>
rn = r.to_numpy()
File "~/.local/lib/python3.7/site-packages/modin/pandas/base.py", line 2962, in to_numpy
arr = self._query_compiler.to_numpy()
File "~/.local/lib/python3.7/site-packages/modin/backends/pandas/query_compiler.py", line 169, in to_numpy
len(arr) != len(self.index) or len(arr[0]) != len(self.columns)
File "~/.local/lib/python3.7/site-packages/modin/error_message.py", line 40, in catch_bugs_and_request_email
" caused this error.\n{}".format(extra_log)
Exception: Internal Error. Please email bug_reports@modin.org with the traceback and command that caused this error.

# Fixed code
def _validate_internal_indices(self, mode=None, **kwargs):
    """
    Validates and optionally updates internal and external indices
    of modin_frame in specified mode. There is 3 modes supported:
        1. "reduced" - force validates on that axes
            where external indices is ["__reduced__"]
        2. "all" - validates indices at all axes, optionally force
            if `force` parameter specified in kwargs
        3. "custom" - validation follows arguments specified in kwargs.

    Parameters
    ----------
        mode : str or bool, default None
        validate_index : bool, (optional, could be specified via `mode`)
        validate_columns : bool, (optional, could be specified via `mode`)
        force : bool (optional, could be specified via `mode`)
            Whether to update external indices with internal if their lengths
            do not match or raise an exception in that case.
    """

    if isinstance(mode, bool):
        is_force = mode
        mode = "all"
    else:
        is_force = kwargs.get("force", False)

    reduced_sample = pandas.Index(["__reduced__"])
    args_dict = {
        "custom": kwargs,
        "reduced": {
            "validate_index": self.index.equals(reduced_sample),
            "validate_columns": self.columns.equals(reduced_sample),
            "force": True,
        },
        "all": {
            "validate_index": True,
            "validate_columns": True,
            "force": is_force,
        },
    }

    args = args_dict.get(mode, args_dict["custom"])

    if args.get("validate_index", True):
        self._validate_axis_equality(axis=0)
    if args.get("validate_columns", True):
        self._validate_axis_equality(axis=1)