TypeError: 'NoneType' object is not iterable about bumpversion HOT 1 OPEN

[bumpversion]
current_version = 0.1.8-rel
commit = False
tag = True
tag_name = 'v{new_version}'
message = 'Bump version: {current_version} → {new_version}'
parse = (?P<major>\d+)\.(?P<minor>\d+)\.(?P<patch>\d+)-{0,1}(?P<release>[a-z]*)
serialize = 
	{major}.{minor}.{patch}-{release}
	{major}.{minor}.{patch}

[bumpversion:part:release]
optional_value = dev
values = 
	dev
	rel

[bumpversion:file:VERSION]
search = {current_version}
replace = {new_version}

[bumpversion:file:README.md]
search = VERSION: {current_version}
replace = {new_version}

[bumpversion:file:src/__init__.py]
search = __version__ == {current_version}
replace = {new_version}

[bumpversion:file:src/app-one/__init__.py]
search = __version__ == {current_version}
replace = {new_version}

[bumpversion:file:src/app-two/__init__.py]
search = __version__ == {current_version}
replace = {new_version}