ruamel.yaml-0.16.10 has change in handling empty keys -> TestYAMLResourceStore.test_empty_key

[mimi1vx]

[  114s] =================================== FAILURES ===================================
[  114s] _____________________ TestYAMLResourceStore.test_empty_key _____________________
[  114s] 
[  114s] self = <translate.storage.test_yaml.TestYAMLResourceStore object at 0x7f000ded55b0>
[  114s] 
[  114s]         def test_empty_key(self):
[  114s]             store = self.StoreClass()
[  114s]             store.parse('''
[  114s]     '': Jedna
[  114s]     foo:
[  114s]       '': Dve
[  114s]     ''')
[  114s]             assert len(store.units) == 2
[  114s]             assert store.units[0].getid() == ''
[  114s]             assert store.units[0].source == 'Jedna'
[  114s]             assert store.units[1].getid() == 'foo->'
[  114s]             assert store.units[1].source == 'Dve'
[  114s]             out = BytesIO()
[  114s]             store.serialize(out)
[  114s] >           assert out.getvalue() == b'''? ''
[  114s]     : Jedna
[  114s]     foo:
[  114s]       ? ''
[  114s]       : Dve
[  114s]     '''
[  114s] E   assert b"'': Jedna\n...\n  '': Dve\n" == b"? ''\n: Jed...''\n  : Dve\n"
[  114s] E     At index 0 diff: b"'" != b'?'
[  114s] E     Full diff:
[  114s] E     - b"'': Jedna\nfoo:\n  '': Dve\n"
[  114s] E     + b"? ''\n: Jedna\nfoo:\n  ? ''\n  : Dve\n"
[  114s] E     ?   ++  ++                 ++  ++++
[  114s] 

[nijel]

The breaking change was actually few releases earlier:

[0, 16, 6]: 2020-01-20
  - fix empty string mapping key roundtripping with preservation of quotes as `? ''`
    (reported via email by Tomer Aharoni).

[nijel]

Fix is here: #3955