setting `theme(axis_text_x=element_blank())` results in an error starting a v0.13.3

[daylinmorgan]

In v0.13.3 setting axis text to element_blank results in an AttributeError.

Minimal reproduction:

from plotnine import (
    ggplot,
    geom_point,
    aes,
    theme,
    element_blank,
)
from plotnine.data import mpg

p = ggplot(mpg, aes("displ", "hwy")) + geom_point()

p.save("plot.svg")
(p + theme(axis_text_x=element_blank())).save("plot-no-x-label.svg")

Output + traceback:

/home/daylin/tmp/repro-plotnine-error/.venv/lib/python3.11/site-packages/plotnine/ggplot.py:604: PlotnineWarning: Saving 6.4 x 4.8 in image.
/home/daylin/tmp/repro-plotnine-error/.venv/lib/python3.11/site-packages/plotnine/ggplot.py:605: PlotnineWarning: Filename: plot.svg
/home/daylin/tmp/repro-plotnine-error/.venv/lib/python3.11/site-packages/plotnine/ggplot.py:604: PlotnineWarning: Saving 6.4 x 4.8 in image.
/home/daylin/tmp/repro-plotnine-error/.venv/lib/python3.11/site-packages/plotnine/ggplot.py:605: PlotnineWarning: Filename: plot-no-x-label.svg
Traceback (most recent call last):
  File "/home/daylin/tmp/repro-plotnine-error/plot.py", line 16, in <module>
    (p + theme(axis_text_x=element_blank())).save("plot-no-x-label.svg")
  File "/home/daylin/tmp/repro-plotnine-error/.venv/lib/python3.11/site-packages/plotnine/ggplot.py", line 661, in save
    sv = self.save_helper(
         ^^^^^^^^^^^^^^^^^
  File "/home/daylin/tmp/repro-plotnine-error/.venv/lib/python3.11/site-packages/plotnine/ggplot.py", line 610, in save_helper
    figure = self.draw(show=False)
             ^^^^^^^^^^^^^^^^^^^^^
  File "/home/daylin/tmp/repro-plotnine-error/.venv/lib/python3.11/site-packages/plotnine/ggplot.py", line 281, in draw
    self._draw_breaks_and_labels()
  File "/home/daylin/tmp/repro-plotnine-error/.venv/lib/python3.11/site-packages/plotnine/ggplot.py", line 458, in _draw_breaks_and_labels
    self.facet.set_limits_breaks_and_labels(panel_params, ax)
  File "/home/daylin/tmp/repro-plotnine-error/.venv/lib/python3.11/site-packages/plotnine/facets/facet.py", line 350, in set_limits_breaks_and_labels
    pad_x = margin.get_as("t", "pt")
            ^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'get_as'

pip list with plotnine==0.13.3:

Package         Version
--------------- -----------
contourpy       1.2.0
cycler          0.12.1
fonttools       4.50.0
kiwisolver      1.4.5
matplotlib      3.8.3
mizani          0.11.1
numpy           1.26.4
packaging       24.0
pandas          2.2.1
patsy           0.5.6
pillow          10.2.0
pip             24.0
plotnine        0.13.3
pyparsing       3.1.2
python-dateutil 2.9.0.post0
pytz            2024.1
scipy           1.12.0
setuptools      65.5.0
six             1.16.0
statsmodels     0.14.1
tzdata          2024.1

I tested with v0.13.2 and did not get the same error.