fix error on no author

example.typ

@@ -1,12 +1,8 @@
 #import "template/template.typ": *
 
 #show: tultemplate2.with(
-  document: "bp",
-  faculty: "fm",
-  title: (cs: "Návod na použití Typst TUL šablony", en: lorem(10)),
-  abstract: (cs: [lorem(100)], en: [lorem(100)]),
+  title: (cs: "Návod na použití Typst TUL šablony"),
   author: "Ondřej Mekina, Matěj Žucha",
-  author_gender: "masculine",
   supervisor: "Ondřej Mekina",
 )
 

template/classic/common.typ

@@ -97,7 +97,9 @@
   // [field_name, field_value, bold]
   let info_fields = (
     ("study_programme", study_programme, false),
-    (if author.contains(", ") { "authors" } else { "author" }, author, true),
+    (
+      if not is_none(author) and author.contains(", ") {"authors" } else { "author" }, author, true
+    ),
     ("supervisor", supervisor, false),
   )
   context {