Merge branch 'release/2.1.0a'
Merge branch 'release/2.1.0a5'
Merge branch 'release/2.1.0b1'
Merge branch 'release/2.1.0b2'
Merge branch 'release/2.1.0'
Merge branch 'release/2.1.1'
Merge branch 'release/2.1.2'
Merge branch 'release/2.1.3'
Merge branch 'release/2.1.4'
Merge branch 'release/2.1.5'
Fix #84 in archive_tw2_resources
Support if_empty and let BoolValidator validate None to False.
2.1.6
Merge branch 'hotfix/2.1.6' into develop