add nil check for parsed_body

[ipc103]

Closes #339

Sometimes, parsing the decoded body will result in a nil value (i.e. if the decoded_body is "null". Here, we only call [] if the parsed_body is something that can respond to it.

Rather than raising a NoMethodError, the parse_body method will return nil if the decoded_body parses to nil.

[choran]

Nice 👍
Tested it locally and all tests pass
Thanks for submitting this

[ipc103]

Awesome - glad I could help!