# Buggy code
def plot_filters(
    self,
    info,
    times=None,
    ch_type=None,
    layout=None,
    vmin=None,
    vmax=None,
    cmap="RdBu_r",
    sensors=True,
    colorbar=True,
    scale=None,
    scale_time=1e3,
    unit="a.u.",
    res=64,
    size=1,
    cbar_fmt="%3.1f",
    name_format="%01d ms",
    proj=False,
    show=True,
    show_names=False,
    title=None,
    mask=None,
    mask_params=None,
    outlines="head",
    contours=6,
    image_interp="bilinear",
    average=None,
    head_pos=None,
):
    """
    Plot topographic filters of the linear model.
    The filters are used to extract discriminant neural sources from
    the measured data (a.k.a. the backward model).

    Parameters
    ----------
    info : instance of Info
        Info dictionary of the epochs used to fit the linear model.
        If not possible, consider using ``create_info``.
    times : float | array of floats | None.
        The time point(s) to plot. If None, the number of ``axes``
        determines the amount of time point(s). If ``axes`` is also None,
        10 topographies will be shown with a regular time spacing between
        the first and last time instant.
    ch_type : 'mag' | 'grad' | 'planar1' | 'planar2' | 'eeg' | None
        The channel type to plot. For 'grad', the gradiometers are
        collected in pairs and the RMS for each pair is plotted.
        If None, then first available channel type from order given
        above is used. Defaults to None.
    layout : None | Layout
        Layout instance specifying sensor positions (does not need to be
        specified for Neuromag data). If possible, the correct layout file
        is inferred from the data; if no appropriate layout file was found
        the layout is automatically generated from the sensor locations.
    vmin : float | callable
        The value specfying the lower bound of the color range.
        If None, and vmax is None, -vmax is used. Else np.min(data).
        If callable, the output equals vmin(data).
    vmax : float | callable
        The value specfying the upper bound of the color range.
        If None, the maximum absolute value is used. If vmin is None,
        but vmax is not, defaults to np.min(data).
        If callable, the output equals vmax(data).
    cmap : matplotlib colormap
        Colormap. For magnetometers and eeg defaults to 'RdBu_r', else
        'Reds'.
    sensors : bool | str
        Add markers for sensor locations to the plot. Accepts matplotlib
        plot format string (e.g., 'r+' for red plusses). If True,
        a circle will be used (via .add_artist). Defaults to True.
    colorbar : bool
        Plot a colorbar.
    scale : dict | float | None
        Scale the data for plotting. If None, defaults to 1e6 for eeg, 1e13
        for grad and 1e15 for mag.
    scale_time : float | None
        Scale the time labels. Defaults to 1e3.
    unit : dict | str | None
        The unit of the channel type used for colorbar label. If
        scale is None the unit is automatically determined.
    res : int
        The resolution of the topomap image (n pixels along each side).
    size : float
        Side length per topomap in inches.
    cbar_fmt : str
        String format for colorbar values.
    name_format : str
        String format for topomap values. Defaults to "%03f ms"
    proj : bool | 'interactive'
        If true SSP projections are applied before display.
        If 'interactive', a check box for reversible selection
        of SSP projection vectors will be show.
    show : bool
        Show figure if True.
    show_names : bool | callable
        If True, show channel names on top of the map. If a callable is
        passed, channel names will be formatted using the callable; e.g.,
        to delete the prefix 'MEG ' from all channel names, pass the
        function lambda x: x.replace('MEG ', ''). If `mask` is not None,
        only significant sensors will be shown.
    title : str | None
        Title. If None (default), no title is displayed.
    mask : ndarray of bool, shape (n_channels, n_times) | None
        The channels to be marked as significant at a given time point.
        Indices set to `True` will be considered. Defaults to None.
    mask_params : dict | None
        Additional plotting parameters for plotting significant sensors.
        Default (None) equals::

            dict(marker='o', markerfacecolor='w', markeredgecolor='k',
                 linewidth=0, markersize=4)

    outlines : 'head' | 'skirt' | dict | None
        The outlines to be drawn. If 'head', the default head scheme will
        be drawn. If 'skirt' the head scheme will be drawn, but sensors are
        allowed to be plotted outside of the head circle. If dict, each key
        refers to a tuple of x and y positions, the values in 'mask_pos'
        will serve as image mask, and the 'autoshrink' (bool) field will
        trigger automated shrinking of the positions due to points outside
        the outline. Alternatively, a matplotlib patch object can be passed
        for advanced masking options, either directly or as a function that
        returns patches (required for multi-axis plots). If None, nothing
        will be drawn. Defaults to 'head'.
    contours : int | False | None
        The number of contour lines to draw.
        If 0, no contours will be drawn.
    image_interp : str
        The image interpolation to be used.
        All matplotlib options are accepted.
    average : float | None
        The time window around a given time to be used for averaging
        (seconds). For example, 0.01 would translate into window that
        starts 5 ms before and ends 5 ms after a given time point.
        Defaults to None, which means no averaging.
    head_pos : dict | None
        If None (default), the sensors are positioned such that they span
        the head circle. If dict, can have entries 'center' (tuple) and
        'scale' (tuple) for what the center and scale of the head
        should be relative to the electrode locations.

    Returns
    -------
    fig : instance of matplotlib.figure.Figure
       The figure.
    """

    from .. import EvokedArray

    if times is None:
        tmin = 0
        times = "auto"
    else:
        tmin = times[0]

    # create an evoked
    filters = EvokedArray(self.filters_.T.reshape(info["nchan"], -1), info, tmin=tmin)
    # the call plot_topomap
    return filters.plot_topomap(
        times=times,
        ch_type=ch_type,
        layout=layout,
        vmin=vmin,
        vmax=vmax,
        cmap=cmap,
        colorbar=colorbar,
        res=res,
        cbar_fmt=cbar_fmt,
        sensors=sensors,
        scale=scale,
        scale_time=scale_time,
        time_format=name_format,
        size=size,
        show_names=show_names,
        unit=unit,
        mask_params=mask_params,
        mask=mask,
        outlines=outlines,
        contours=contours,
        title=title,
        image_interp=image_interp,
        show=show,
        head_pos=head_pos,
    )


# 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_filters(
    self,
    info,
    times=None,
    ch_type=None,
    layout=None,
    vmin=None,
    vmax=None,
    cmap="RdBu_r",
    sensors=True,
    colorbar=True,
    scale=None,
    scale_time=1e3,
    unit="a.u.",
    res=64,
    size=1,
    cbar_fmt="%3.1f",
    name_format="%01d ms",
    proj=False,
    show=True,
    show_names=False,
    title=None,
    mask=None,
    mask_params=None,
    outlines="head",
    contours=6,
    image_interp="bilinear",
    average=None,
    head_pos=None,
):
    """
    Plot topographic filters of the linear model.
    The filters are used to extract discriminant neural sources from
    the measured data (a.k.a. the backward model).

    Parameters
    ----------
    info : instance of Info
        Info dictionary of the epochs used to fit the linear model.
        If not possible, consider using ``create_info``.
    times : float | array of floats | None.
        The time point(s) to plot. If None, the number of ``axes``
        determines the amount of time point(s). If ``axes`` is also None,
        10 topographies will be shown with a regular time spacing between
        the first and last time instant.
    ch_type : 'mag' | 'grad' | 'planar1' | 'planar2' | 'eeg' | None
        The channel type to plot. For 'grad', the gradiometers are
        collected in pairs and the RMS for each pair is plotted.
        If None, then first available channel type from order given
        above is used. Defaults to None.
    layout : None | Layout
        Layout instance specifying sensor positions (does not need to be
        specified for Neuromag data). If possible, the correct layout file
        is inferred from the data; if no appropriate layout file was found
        the layout is automatically generated from the sensor locations.
    vmin : float | callable
        The value specfying the lower bound of the color range.
        If None, and vmax is None, -vmax is used. Else np.min(data).
        If callable, the output equals vmin(data).
    vmax : float | callable
        The value specfying the upper bound of the color range.
        If None, the maximum absolute value is used. If vmin is None,
        but vmax is not, defaults to np.min(data).
        If callable, the output equals vmax(data).
    cmap : matplotlib colormap | (colormap, bool) | 'interactive' | None
        Colormap to use. If tuple, the first value indicates the colormap
        to use and the second value is a boolean defining interactivity. In
        interactive mode the colors are adjustable by clicking and dragging
        the colorbar with left and right mouse button. Left mouse button
        moves the scale up and down and right mouse button adjusts the
        range. Hitting space bar resets the range. Up and down arrows can
        be used to change the colormap. If None, 'Reds' is used for all
        positive data, otherwise defaults to 'RdBu_r'. If 'interactive',
        translates to (None, True). Defaults to 'RdBu_r'.

        .. warning::  Interactive mode works smoothly only for a small
            amount of topomaps.

    sensors : bool | str
        Add markers for sensor locations to the plot. Accepts matplotlib
        plot format string (e.g., 'r+' for red plusses). If True,
        a circle will be used (via .add_artist). Defaults to True.
    colorbar : bool
        Plot a colorbar.
    scale : dict | float | None
        Scale the data for plotting. If None, defaults to 1e6 for eeg, 1e13
        for grad and 1e15 for mag.
    scale_time : float | None
        Scale the time labels. Defaults to 1e3.
    unit : dict | str | None
        The unit of the channel type used for colorbar label. If
        scale is None the unit is automatically determined.
    res : int
        The resolution of the topomap image (n pixels along each side).
    size : float
        Side length per topomap in inches.
    cbar_fmt : str
        String format for colorbar values.
    name_format : str
        String format for topomap values. Defaults to "%03f ms"
    proj : bool | 'interactive'
        If true SSP projections are applied before display.
        If 'interactive', a check box for reversible selection
        of SSP projection vectors will be show.
    show : bool
        Show figure if True.
    show_names : bool | callable
        If True, show channel names on top of the map. If a callable is
        passed, channel names will be formatted using the callable; e.g.,
        to delete the prefix 'MEG ' from all channel names, pass the
        function lambda x: x.replace('MEG ', ''). If `mask` is not None,
        only significant sensors will be shown.
    title : str | None
        Title. If None (default), no title is displayed.
    mask : ndarray of bool, shape (n_channels, n_times) | None
        The channels to be marked as significant at a given time point.
        Indices set to `True` will be considered. Defaults to None.
    mask_params : dict | None
        Additional plotting parameters for plotting significant sensors.
        Default (None) equals::

            dict(marker='o', markerfacecolor='w', markeredgecolor='k',
                 linewidth=0, markersize=4)

    outlines : 'head' | 'skirt' | dict | None
        The outlines to be drawn. If 'head', the default head scheme will
        be drawn. If 'skirt' the head scheme will be drawn, but sensors are
        allowed to be plotted outside of the head circle. If dict, each key
        refers to a tuple of x and y positions, the values in 'mask_pos'
        will serve as image mask, and the 'autoshrink' (bool) field will
        trigger automated shrinking of the positions due to points outside
        the outline. Alternatively, a matplotlib patch object can be passed
        for advanced masking options, either directly or as a function that
        returns patches (required for multi-axis plots). If None, nothing
        will be drawn. Defaults to 'head'.
    contours : int | False | None
        The number of contour lines to draw.
        If 0, no contours will be drawn.
    image_interp : str
        The image interpolation to be used.
        All matplotlib options are accepted.
    average : float | None
        The time window around a given time to be used for averaging
        (seconds). For example, 0.01 would translate into window that
        starts 5 ms before and ends 5 ms after a given time point.
        Defaults to None, which means no averaging.
    head_pos : dict | None
        If None (default), the sensors are positioned such that they span
        the head circle. If dict, can have entries 'center' (tuple) and
        'scale' (tuple) for what the center and scale of the head
        should be relative to the electrode locations.

    Returns
    -------
    fig : instance of matplotlib.figure.Figure
       The figure.
    """

    from .. import EvokedArray

    if times is None:
        tmin = 0
        times = "auto"
    else:
        tmin = times[0]

    # create an evoked
    filters = EvokedArray(self.filters_.T.reshape(info["nchan"], -1), info, tmin=tmin)
    # the call plot_topomap
    return filters.plot_topomap(
        times=times,
        ch_type=ch_type,
        layout=layout,
        vmin=vmin,
        vmax=vmax,
        cmap=cmap,
        colorbar=colorbar,
        res=res,
        cbar_fmt=cbar_fmt,
        sensors=sensors,
        scale=scale,
        scale_time=scale_time,
        time_format=name_format,
        size=size,
        show_names=show_names,
        unit=unit,
        mask_params=mask_params,
        mask=mask,
        outlines=outlines,
        contours=contours,
        title=title,
        image_interp=image_interp,
        show=show,
        head_pos=head_pos,
    )