# Buggy code
def reindex(
    self,
    major=None,
    items=None,
    minor=None,
    method=None,
    major_axis=None,
    minor_axis=None,
    copy=True,
):
    """
    Conform panel to new axis or axes

    Parameters
    ----------
    major : Index or sequence, default None
        Can also use 'major_axis' keyword
    items : Index or sequence, default None
    minor : Index or sequence, default None
        Can also use 'minor_axis' keyword
    method : {'backfill', 'bfill', 'pad', 'ffill', None}, default None
        Method to use for filling holes in reindexed Series

        pad / ffill: propagate last valid observation forward to next valid
        backfill / bfill: use NEXT valid observation to fill gap
    copy : boolean, default True
        Return a new object, even if the passed indexes are the same

    Returns
    -------
    Panel (new object)
    """
    result = self

    major = _mut_exclusive(major, major_axis)
    minor = _mut_exclusive(minor, minor_axis)

    if major is not None:
        result = result._reindex_axis(major, method, 1, copy)

    if minor is not None:
        result = result._reindex_axis(minor, method, 2, copy)

    if items is not None:
        result = result._reindex_axis(items, method, 0, copy)

    if result is self and copy:
        raise ValueError("Must specify at least one axis")

    return result


# Traceback (IndexError)
In [1]: from pandas import *

In [2]: a = DataFrame(columns=['column1'], data=[1])

In [3]: b = DataFrame(columns=['column1'])

In [4]: a.merge(b, on=['column1'], how='left')


IndexError                                Traceback (most recent call last)
IndexError: index out of range for array

# Fixed code
def reindex(
    self,
    major=None,
    items=None,
    minor=None,
    method=None,
    major_axis=None,
    minor_axis=None,
    copy=True,
):
    """
    Conform panel to new axis or axes

    Parameters
    ----------
    major : Index or sequence, default None
        Can also use 'major_axis' keyword
    items : Index or sequence, default None
    minor : Index or sequence, default None
        Can also use 'minor_axis' keyword
    method : {'backfill', 'bfill', 'pad', 'ffill', None}, default None
        Method to use for filling holes in reindexed Series

        pad / ffill: propagate last valid observation forward to next valid
        backfill / bfill: use NEXT valid observation to fill gap
    copy : boolean, default True
        Return a new object, even if the passed indexes are the same

    Returns
    -------
    Panel (new object)
    """
    result = self

    major = _mut_exclusive(major, major_axis)
    minor = _mut_exclusive(minor, minor_axis)

    if (
        method is None
        and not self._is_mixed_type
        and com._count_not_none(items, major, minor) == 3
    ):
        return self._reindex_multi(items, major, minor)

    if major is not None:
        result = result._reindex_axis(major, method, 1, copy)

    if minor is not None:
        result = result._reindex_axis(minor, method, 2, copy)

    if items is not None:
        result = result._reindex_axis(items, method, 0, copy)

    if result is self and copy:
        raise ValueError("Must specify at least one axis")

    return result