Error when plotting using matplotlib

[JordiBForgeFlow]

Prerequisites
Describe the bug

Error
Using neuralprophet > 0.5.4, when attempting to print plots using matplotlib we get an error:
AttributeError: 'None' object has no attribute 'canvas'

This is caused when this line was changed:
https://github.com/ourownstory/neural_prophet/blame/main/neuralprophet/plot_model_parameters_matplotlib.py#L140C15-L140C29

in e27b5b0

fig = fig.tight_layout()

The method tight_layout of matplotlib does not do any return at all. See https://github.com/matplotlib/matplotlib/blob/v3.5.x/lib/matplotlib/figure.py#L3201

To Reproduce
model.set_plotting_backend("matplotlib")
forecast_figure = model.plot(forecast)

Expected behavior

The plots are generated in matplotlib

What actually happens

The call:
fig = fig.tight_layout()

Returns fig = None