diff --git a/src/symbols/list.rs b/src/symbols/list.rs
index 5925971..2df3247 100644
--- a/src/symbols/list.rs
+++ b/src/symbols/list.rs
@@ -48,6 +48,8 @@ impl Symbol for List<'_> {
     for symbol in &self.symbols {
       if let Some(provides) = symbol.provides() {
         r.extend(provides.into_iter());
+      } else {
+        return None;
       }
     }
     if r.is_empty() {