Issue with pick_types(emg=True)

Describe the bug

We get an error of “No Data channels found” when selecting emg channels with picks=['emg'] in a dataset which contains only emg channels.

Steps to reproduce

together with @jasmainak and @simonatemereanca we wrote this script: https://gist.github.com/TariqCannonier/0c708ae01268bfbb766bd320eac45035 to reproduce the bug.

Expected results

Should plot PSD for EMG channels only

Actual results

  File "<ipython-input-7-ad302adea22f>", line 1, in <module>
    runfile('/Users/tariqcannonier/.spyder-py3/temp.py', wdir='/Users/tariqcannonier/.spyder-py3')

  File "/Users/tariqcannonier/anaconda3/lib/python3.7/site-packages/spyder_kernels/customize/spydercustomize.py", line 827, in runfile
    execfile(filename, namespace)

  File "/Users/tariqcannonier/anaconda3/lib/python3.7/site-packages/spyder_kernels/customize/spydercustomize.py", line 110, in execfile
    exec(compile(f.read(), filename, 'exec'), namespace)

  File "/Users/tariqcannonier/.spyder-py3/temp.py", line 20, in <module>
    raw.plot_psd(picks=['emg'])

  File "</Users/tariqcannonier/anaconda3/lib/python3.7/site-packages/mne/externals/decorator.py:decorator-gen-147>", line 2, in plot_psd

  File "/Users/tariqcannonier/anaconda3/lib/python3.7/site-packages/mne/utils/_logging.py", line 90, in wrapper
    return function(*args, **kwargs)

  File "/Users/tariqcannonier/anaconda3/lib/python3.7/site-packages/mne/io/base.py", line 1585, in plot_psd
    spatial_colors=spatial_colors, verbose=verbose)

  File "</Users/tariqcannonier/anaconda3/lib/python3.7/site-packages/mne/externals/decorator.py:decorator-gen-133>", line 2, in plot_raw_psd

  File "/Users/tariqcannonier/anaconda3/lib/python3.7/site-packages/mne/utils/_logging.py", line 90, in wrapper
    return function(*args, **kwargs)

  File "/Users/tariqcannonier/anaconda3/lib/python3.7/site-packages/mne/viz/raw.py", line 621, in plot_raw_psd
    raw.info, proj, picks, ax, area_mode)

  File "/Users/tariqcannonier/anaconda3/lib/python3.7/site-packages/mne/viz/utils.py", line 3005, in _set_psd_plot_params
    raise RuntimeError('No data channels found')

RuntimeError: No data channels found

Additional information

My system information is here:

Platform:      Darwin-15.6.0-x86_64-i386-64bit
Python:        3.7.4 (default, Aug 13 2019, 15:17:50)  [Clang 4.0.1 (tags/RELEASE_401/final)]
Executable:    /Users/tariqcannonier/anaconda3/bin/python
CPU:           i386: 4 cores
Memory:        8.0 GB

mne:           0.20.dev0
numpy:         1.17.2 {blas=mkl_rt, lapack=mkl_rt}
scipy:         1.3.1
matplotlib:    3.1.1 {backend=MacOSX}

sklearn:       0.21.3
numba:         0.45.1
nibabel:       2.5.1
cupy:          Not found
pandas:        0.25.2
dipy:          1.0.0
mayavi:        4.7.1 {qt_api=pyqt5, PyQt5=5.10.1}
pyvista:       0.22.4
vtk:           8.1.2
None

[larsoner]

The problem is that it’s not just M/EEG, but also (at least) sEEG, ECoG, and fNIRS. So I’d rather say in the docs (maybe glossary?) what “data channels” are, that way if we add a new “data channel” we have fewer places that need updating.

[larsoner]

@drammock fixed this in #7668