caching: pickle.load() fails

[ZelenyMartin]

Conditions

Cache level 3 needs to be enabled in ~/.nitrate:

[cache]
level = 3

Test suite fail

python -m nitrate.tests
Output from test suite (needs to be run as whole test suite - no just the CasePlan test case - it does not fail)

CasePlan
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sort key update ... ERROR

======================================================================
ERROR: Sort key update
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/home/mzeleny/Work/git/python-nitrate/venv/lib64/python3.8/site-packages/nitrate/tests.py", line 1230, in test_sortkey_update
 cache.load()
 File "/home/mzeleny/Work/git/python-nitrate/venv/lib64/python3.8/site-packages/nitrate/cache.py", line 298, in load
 data = pickle.load(input_file)
TypeError: __new__() missing 1 required positional argument: 'object'

----------------------------------------------------------------------
Ran 1 test in 1.360s

FAILED (errors=1)

Production using fail

Traceback (most recent call last):
 File "./progress-generator.py", line 296, in <module>
 main()
 File "./progress-generator.py", line 282, in main
 dontRemoveCompose.append(updateComposeDetailPage(processedConfig['TCMS_STATUSES'], wikiPage, compose, tag))
 File "./progress-generator.py", line 223, in updateComposeDetailPage
 tcmsPart, exitCode = getTcmsInfo(tcmsStatuses, compose, tag)
 File "./progress-generator.py", line 126, in getTcmsInfo
 TRs=nitrate.TestRun.search(build__name=build, tag__name__contains=tag)
 File "/usr/lib/python3.8/site-packages/nitrate/mutable.py", line 538, in search
 return [TestRun(hash)
 File "/usr/lib/python3.8/site-packages/nitrate/mutable.py", line 538, in <listcomp>
 return [TestRun(hash)
 File "/usr/lib/python3.8/site-packages/nitrate/base.py", line 311, in __new__
 Cache()
 File "/usr/lib/python3.8/site-packages/nitrate/cache.py", line 194, in __new__
 cls._instance.__init__(*args, **kwargs)
 File "/usr/lib/python3.8/site-packages/nitrate/cache.py", line 203, in __init__
 self.enter(filename)
 File "/usr/lib/python3.8/site-packages/nitrate/cache.py", line 388, in enter
 self.load()
 File "/usr/lib/python3.8/site-packages/nitrate/cache.py", line 298, in load
 data = pickle.load(input_file)
TypeError: __new__() missing 1 required positional argument: 'object'

[ZelenyMartin]

Closest case found: https://bugs.python.org/issue18359

If some class objects have extra arguments in the new constructor , pickle fail to serialize it.

I tried also other python modules like json, marshal and shelve but without success.