# Buggy code
def _plot_topomap_multi_cbar(
    data,
    pos,
    ax,
    title=None,
    unit=None,
    vmin=None,
    vmax=None,
    cmap="RdBu_r",
    colorbar=False,
    cbar_fmt="%3.3f",
):
    """Aux Function"""
    import matplotlib.pyplot as plt
    from mpl_toolkits.axes_grid1 import make_axes_locatable

    _hide_frame(ax)
    vmin = np.min(data) if vmin is None else vmin
    vmax = np.max(data) if vmax is None else vmax

    if title is not None:
        ax.set_title(title, fontsize=10)
    im, _ = plot_topomap(
        data,
        pos,
        vmin=vmin,
        vmax=vmax,
        axes=ax,
        cmap=cmap,
        image_interp="bilinear",
        contours=False,
        show=False,
    )

    if colorbar is True:
        divider = make_axes_locatable(ax)
        cax = divider.append_axes("right", size="10%", pad=0.25)
        cbar = plt.colorbar(im, cax=cax, format=cbar_fmt)
        cbar.set_ticks((vmin, vmax))
        if unit is not None:
            cbar.ax.set_title(unit, fontsize=8)
        cbar.ax.tick_params(labelsize=8)


# Traceback (ValueError)
n [15]: Traceback (most recent call last):
File "/tsi/doctorants/mainak/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_qt5.py", line 291, in mouseReleaseEvent
FigureCanvasBase.button_release_event(self, x, y, button)
File "/tsi/doctorants/mainak/anaconda/lib/python2.7/site-packages/matplotlib/backend_bases.py", line 1891, in button_release_event
self.callbacks.process(s, event)
File "/tsi/doctorants/mainak/anaconda/lib/python2.7/site-packages/matplotlib/cbook.py", line 533, in process
proxy(*args, **kwargs)
File "/tsi/doctorants/mainak/anaconda/lib/python2.7/site-packages/matplotlib/cbook.py", line 408, in __call__
return mtd(*args, **kwargs)
File "/tsi/doctorants/mainak/anaconda/lib/python2.7/site-packages/matplotlib/widgets.py", line 1250, in release
self.onselect(vmin, vmax)
File "/tsi/doctorants/mainak/mne-python/mne/viz/evoked.py", line 90, in _butterfly_onselect
layout=None)
File "/tsi/doctorants/mainak/mne-python/mne/viz/topomap.py", line 49, in _prepare_topo_plot
picks, pos = _pair_grad_sensors(info, layout)
File "/tsi/doctorants/mainak/mne-python/mne/channels/layout.py", line 689, in _pair_grad_sensors
raise ValueError("No 'grad' channel pairs found.")
ValueError: No 'grad' channel pairs found.

# Fixed code
def _plot_topomap_multi_cbar(
    data,
    pos,
    ax,
    title=None,
    unit=None,
    vmin=None,
    vmax=None,
    cmap=None,
    outlines="head",
    colorbar=False,
    cbar_fmt="%3.3f",
):
    """Aux Function"""
    import matplotlib.pyplot as plt
    from mpl_toolkits.axes_grid1 import make_axes_locatable

    _hide_frame(ax)
    vmin = np.min(data) if vmin is None else vmin
    vmax = np.max(data) if vmax is None else vmax

    if cmap == "interactive":
        cmap = (None, True)
    elif not isinstance(cmap, tuple):
        cmap = (cmap, True)
    if title is not None:
        ax.set_title(title, fontsize=10)
    im, _ = plot_topomap(
        data,
        pos,
        vmin=vmin,
        vmax=vmax,
        axes=ax,
        cmap=cmap[0],
        image_interp="bilinear",
        contours=False,
        outlines=outlines,
        show=False,
    )

    if colorbar is True:
        divider = make_axes_locatable(ax)
        cax = divider.append_axes("right", size="10%", pad=0.25)
        cbar = plt.colorbar(im, cax=cax, format=cbar_fmt)
        cbar.set_ticks((vmin, vmax))
        if unit is not None:
            cbar.ax.set_title(unit, fontsize=8)
        cbar.ax.tick_params(labelsize=8)
        if cmap[1]:
            ax.CB = DraggableColorbar(cbar, im)