From 901270ae70a1a38c8c349f58ae3b0b980fa63d57 Mon Sep 17 00:00:00 2001
From: Bodil Stokke <bodil@bodil.org>
Date: Fri, 6 Apr 2018 15:29:32 +0100
Subject: [PATCH] Fix integer underflow situation on empty lists.

---
 src/vector.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/vector.rs b/src/vector.rs
index 8a916a9..85a3afb 100644
--- a/src/vector.rs
+++ b/src/vector.rs
@@ -206,7 +206,11 @@ impl<A> Vector<A> {
     ///
     /// Time: O(log n)
     pub fn last(&self) -> Option<Arc<A>> {
-        self.get(self.len() - 1)
+        if self.is_empty() {
+            None
+        } else {
+            self.get(self.len() - 1)
+        }
     }
 
     /// Get the vector without the last element.