Conversion to Numeric by adding 0 to String fails for '0' padded values '08' and '09'

puppet apply -e 'notify{"result: ${'04' + 0}": }'

Notice: Compiled catalog for test.local in environment production in 0.05 seconds

Notice: result: 4

Notice: /Stage[main]/Main/Notify[result: 4]/message: defined 'message' as 'result: 4'

Notice: Applied catalog in 0.26 seconds

puppet apply -e 'notify{"result: ${'08' + 0}": }'

Error: Could not parse for environment production: Not a valid octal number 08  at line 1:19 on node test.local