diff --git a/src/storage_proofs.rs b/src/storage_proofs.rs
index 8033fea..4a8cce1 100644
--- a/src/storage_proofs.rs
+++ b/src/storage_proofs.rs
@@ -133,7 +133,7 @@ impl StorageProofs {
                                         builder.push_input(name, decode_u256(val)?);
                                     }
                                 },
-                                None => todo!(),
+                                _ => return Err("expected inner array of u256".to_string()),
                             }
                         }
                     } else {