Allow optional values in JSON

src/functions.liq

@@ -27,11 +27,11 @@ def build_metadata(json_string) =
             playlist_id: int,
             playlist_item: string,
             track_type: int,
-            track_start: string,
-            track_duration: int,
-            track_title: string,
-            track_album: string,
-            track_artist: string,
+            track_start: string?,
+            track_duration: int?,
+            track_title: string?,
+            track_album: string?,
+            track_artist: string?
         }) = json_string
     [
         ("show_name", data.show_name),
@@ -40,11 +40,11 @@ def build_metadata(json_string) =
         ("playlist_id", "#{data.playlist_id}"),
         ("playlist_item", "#{data.playlist_item}"),
         ("track_type", "#{data.track_type}"),
-        ("track_start", data.track_start),
+        ("track_start", "#{data.track_start}"),
         ("track_duration", "#{data.track_duration}"),
-        ("track_title", data.track_title),
-        ("track_album", data.track_album),
-        ("track_artist", data.track_artist),
+        ("track_title", "#{data.track_title}"),
+        ("track_album", "#{data.track_album}"),
+        ("track_artist", "#{data.track_artist}"),
     ]
 end