Quality-filter "'NoneType' object is not subscriptable"

Hello,

I'm trying to use q2 quality-filter on the Mockrobiota 'Extreme' data (mock-12) before denoising with deblur, using the command

qiime quality-filter q-score \
--i-demux demuxed_sequences.qza \
--o-filtered-sequences quality_filtered_seqs.qza \
--o-filter-stats quality_filtered_stats.qza \
--verbose

However, I get the following error when I try to run it on my data:

Traceback (most recent call last):
File "/home/dylan/miniconda3/envs/qiime2-2021.11/lib/python3.8/site-packages/q2cli/commands.py", line 339, in call
results = action(**arguments)
File "", line 2, in q_score
File "/home/dylan/miniconda3/envs/qiime2-2021.11/lib/python3.8/site-packages/qiime2/sdk/action.py", line 245, in bound_callable
outputs = self.callable_executor(scope, callable_args,
File "/home/dylan/miniconda3/envs/qiime2-2021.11/lib/python3.8/site-packages/qiime2/sdk/action.py", line 391, in callable_executor
output_views = self._callable(**view_args)
File "/home/dylan/miniconda3/envs/qiime2-2021.11/lib/python3.8/site-packages/q2_quality_filter/_filter.py", line 90, in q_score
phred_offset = yaml.load(metadata_view,
TypeError: 'NoneType' object is not subscriptable
Plugin error from quality-filter:
'NoneType' object is not subscriptable
See above for debug info.

This error occurs in both the 2021.4 and 2021.11 release.

Can anyone shed some light on this?