Can't use `?:` inside ${} without quote

[hiroyuki-sato]

• Digdag 0.9.21

NG (Without quote)

timezone: UTC

_export:
  hoge: 123

+task1:
  echo>: ${hoge ? true : false}

2017-12-08 09:28:51 +0900: Digdag v0.9.21
error: Validating project failed
workflow /private/tmp/test/test.dig mapping values are not allowed here
 in 'string', line 7, column 24:
      echo>: ${hoge ? true : false}
                           ^
 (model validation)

Workdaround

Quotng ${} with "

timezone: UTC

_export:
  hoge: 123

+task1:
  echo>: "${hoge ? true : false}"

true