Using @export(output="none") breaks with cache enabled

[twiggler]

Reproduction:

• Enable cache
• Run test_unsupported_fs

It fails with:

FAILED tests/plugins/filesystem/test_icat.py::test_unsupported_fs - AssertionError: assert <generator object CacheWriter.__iter__ at 0x7f3e2db1b9f0> is None

Note that the iter fix did not cause this because the prior behavior was to fail with

AssertionError: assert <dissect.target.helpers.cache.CacheWriter object at 0x7a65819f70b0> is None

Impact
When using the cache, plugins using @export(None) are broken.
List of plugins:

• icat
• exchange
• rdpcache
• windows defender
• esxconf
• loaders