Handle puncuation-only search options.

src/parser/regular_link.rs

@@ -262,7 +262,7 @@ fn file_path_reg<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, PathReg<'s>> {
             search_option: search_option
                 .map(Into::<&str>::into)
                 .map(Into::<Cow<str>>::into),
-            application: todo!(),
+            application: None, // TODO
         },
     ))
 }