Liquid Soap 1.1 vs 1.3 - Dynamic playlist - liquidsoap

Question

Scenario:
Ubuntu 17.04
Liquid Soap 1.1.1 installed by apt-get
Liquid Soap 1.3.1 installed by OPAM
On 1.1.1, I cannot use AAC+ encoder. So I've installed 1.3.1 with AAC+ support. But using a same .liq file, both versions act different.
For some reason, 1.1 works, 1.3 not:
def my_request_function() =
# Get the first line of my external process
result = list.hd(get_process_lines("php -q liquid.php"))
# Create and return a request using this result
request.create(result)
end
Error:
At line 17, char 24:
this value has type
(default:_)->_ (inferred at line 15, char 19-58)
but it should be a subtype of
string
I want to read the "next song" from a PHP script. On 1.1.1 works with MP3 (+icecast2), but since I need AAC+, I'm using 1.3.1, that I cannot figure out how to read the external script.
Any ideas? Thank you.

Answer 1

1.3 had another argument added to list.hd and other list functions.
https://github.com/savonet/liquidsoap/blob/master/CHANGES#L52
You can update your code with the new default value argument and it should work.
result = list.hd(default="", get_process_lines("php -q liquid.php"))