Fix unused ElementType

[tiagovla]

Fixes #2377.

[tiagovla]

Running:

pytest test/unit/fem/test_mixed_element.py::test_mixed_element

Results in:

FAILED test/unit/fem/test_mixed_element.py::test_mixed_element[FiniteElement-Lag
range-1-cell0] - TypeError: 'NoneType' object is not iterable
#...

This error happens in:

dolfinx/python/dolfinx/fem/forms.py

Lines 132 to 136 in 3133fb6

	for integral_type, data in sd.get(domain).items():
	# Check that the subdomain data for each integral of this type is
	# the same
	assert all([id(d) == id(data[0]) for d in data])
	subdomains[integral_type] = data[0]

since sd.get(domain) = {'cell': None}. Checking if data is not None fixes it.

Maybe there's something else missing that I'm not aware.

[garth-wells]

@jpdean is this related to your recent chages?

[jpdean]

Yes, I'll take a look

[jpdean]

@tiagovla I am unable to reproduce this error with your test. For me, sd.get(domain) returns {'cell': [None]}, as expected. Are you using the latest version of UFL?

[tiagovla]

@tiagovla I am unable to reproduce this error with your test. For me, sd.get(domain) returns {'cell': [None]}, as expected. Are you using the latest version of UFL?

That was it! I had #4e3868d. After upgrading it, the test passed.