Error when plotting signal with 3 navigation dimensions

[magnunor]

Using the most recent RELEASE_next_major in HyperSpy, most recent main in hyperspy_gui_ipywidgets and hyperspy_gui_traitsui. The following gives an error in JupyterLab:

%matplotlib widget
import numpy as np
import hyperspy.api as hs
s = hs.signals.Signal2D(np.random.random((5, 10, 10, 20, 20)))
s.plot()

The error:

hyperspy_gui_traitsui/hyperspy_gui_traitsui/__init__.py:94
     90 elif ETSConfig.toolkit == "":
     91     # The toolkit has not been set and no supported toolkit is available, so
     92     # setting it to "null"
     93     set_ets_toolkit("null")
---> 94     if preferences.GUIs.warn_if_guis_are_missing:
     95         _logger.warning(
     96             f"The {backend} matplotlib backend is not compatible with the "
     97             "traitsui GUI elements. For more information, read "
     98             "http://hyperspy.readthedocs.io/en/stable/user_guide/getting_started.html#possible-warnings-when-importing-hyperspy"
     99             ".")

AttributeError: 'GUIs' object has no attribute 'warn_if_guis_are_missing'

Running the s.plot() again does not give an error.

---

The following does not give an error (in JupyterLab):

%matplotlib widget
import numpy as np
import hyperspy.api as hs
s = hs.signals.Signal2D(np.random.random((10, 10, 20, 20)))
s.plot()

---

The following does not give an error (in JupyterLab):

%matplotlib qt5
import numpy as np
import hyperspy.api as hs
s = hs.signals.Signal2D(np.random.random((5, 10, 10, 20, 20)))
s.plot()

---

I'm guessing it is due to this line: https://github.com/hyperspy/hyperspy_gui_traitsui/blob/main/hyperspy_gui_traitsui/__init__.py#L94

However, I'm guessing there is something strange going on elsewhere, as it only happens with the signal with 3 navigation dimensions.

[ericpre]

This should be in fixed in #58 and not merged yet to avoid having to deal with a separate branch for the RELEASE_next_branch of hyperspy.