<RuleError: error code 4

[tnickl]

File "/usr/local/bin/pykwalify", line 8, in
sys.exit(cli_entrypoint())
File "/usr/local/lib/python3.9/site-packages/pykwalify/cli.py", line 98, in cli_entrypoint
run(parse_cli())
File "/usr/local/lib/python3.9/site-packages/pykwalify/cli.py", line 85, in run
c.validate()
File "/usr/local/lib/python3.9/site-packages/pykwalify/core.py", line 183, in validate
self._start_validate(self.source)
File "/usr/local/lib/python3.9/site-packages/pykwalify/core.py", line 225, in _start_validate
root_rule = Rule(schema=self.schema)
File "/usr/local/lib/python3.9/site-packages/pykwalify/rule.py", line 66, in init
self.init(schema, "")
File "/usr/local/lib/python3.9/site-packages/pykwalify/rule.py", line 443, in init
func_mapping[k](v, rule, path)
File "/usr/local/lib/python3.9/site-packages/pykwalify/rule.py", line 1188, in init_mapping_value
rule.init(v, u"{0}/mapping/{1}".format(path, k))
File "/usr/local/lib/python3.9/site-packages/pykwalify/rule.py", line 443, in init
func_mapping[k](v, rule, path)
File "/usr/local/lib/python3.9/site-packages/pykwalify/rule.py", line 786, in init_required_value
raise RuleError(
pykwalify.errors.RuleError: <RuleError: error code 4: Value: 'yes' for required keyword must be a boolean: Path: '/mapping/region'>

Why does this error show up ?