# Buggy code
def take_2d_multi(arr, row_idx, col_idx, fill_value=np.nan):
    dtype_str = arr.dtype.name

    out_shape = len(row_idx), len(col_idx)

    if dtype_str in ("int32", "int64", "bool"):
        row_mask = row_idx == -1
        col_mask = col_idx == -1
        needs_masking = row_mask.any() or col_mask.any()

        if needs_masking:
            return take_2d_multi(
                _maybe_upcast(arr), row_idx, col_idx, fill_value=fill_value
            )
        else:
            out = np.empty(out_shape, dtype=arr.dtype)
            take_f = _get_take2d_function(dtype_str, axis="multi")
            take_f(
                arr,
                _ensure_int64(row_idx),
                _ensure_int64(col_idx),
                out=out,
                fill_value=fill_value,
            )
            return out
    elif dtype_str in ("float64", "object", "datetime64[ns]"):
        out = np.empty(out_shape, dtype=arr.dtype)
        take_f = _get_take2d_function(dtype_str, axis="multi")
        take_f(
            arr,
            _ensure_int64(row_idx),
            _ensure_int64(col_idx),
            out=out,
            fill_value=fill_value,
        )
        return out
    else:
        return take_2d(
            take_2d(arr, row_idx, axis=0, fill_value=fill_value),
            col_idx,
            axis=1,
            fill_value=fill_value,
        )


# 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 take_2d_multi(arr, row_idx, col_idx, fill_value=np.nan, out=None):
    dtype_str = arr.dtype.name

    out_shape = len(row_idx), len(col_idx)

    if dtype_str in ("int32", "int64", "bool"):
        row_mask = row_idx == -1
        col_mask = col_idx == -1
        needs_masking = row_mask.any() or col_mask.any()

        if needs_masking:
            return take_2d_multi(
                _maybe_upcast(arr), row_idx, col_idx, fill_value=fill_value, out=out
            )
        else:
            if out is None:
                out = np.empty(out_shape, dtype=arr.dtype)
            take_f = _get_take2d_function(dtype_str, axis="multi")
            take_f(
                arr,
                _ensure_int64(row_idx),
                _ensure_int64(col_idx),
                out=out,
                fill_value=fill_value,
            )
            return out
    elif dtype_str in ("float64", "object", "datetime64[ns]"):
        if out is None:
            out = np.empty(out_shape, dtype=arr.dtype)
        take_f = _get_take2d_function(dtype_str, axis="multi")
        take_f(
            arr,
            _ensure_int64(row_idx),
            _ensure_int64(col_idx),
            out=out,
            fill_value=fill_value,
        )
        return out
    else:
        if out is not None:
            raise ValueError("Cannot pass out in this case")

        return take_2d(
            take_2d(arr, row_idx, axis=0, fill_value=fill_value),
            col_idx,
            axis=1,
            fill_value=fill_value,
        )