Prevent get and get_mut from panicking

In contrast to direct indexing, the use of get and get_mut is generally
expected not to panic (as practiced by std collections).

src/lib.rs

@@ -324,7 +324,7 @@ where
         K: Borrow<Q>,
         Q: Eq + Hash,
     {
-        self.inner.get(k).map(|v| &v[0])
+        self.inner.get(k)?.get(0)
     }
 
     /// Returns a mutable reference to the first item in the vector corresponding to
@@ -351,7 +351,7 @@ where
         K: Borrow<Q>,
         Q: Eq + Hash,
     {
-        self.inner.get_mut(k).map(|v| v.get_mut(0).unwrap())
+        self.inner.get_mut(k)?.get_mut(0)
     }
 
     /// Returns a reference to the vector corresponding to the key.
@@ -1077,6 +1077,14 @@ mod tests {
         assert_eq!(m.get(&1), Some(&42));
     }
 
+    #[test]
+    fn get_empty() {
+        let mut m: MultiMap<usize, usize> = MultiMap::new();
+        m.insert(1, 42);
+        m.get_vec_mut(&1).and_then(Vec::pop);
+        assert_eq!(m.get(&1), None);
+    }
+
     #[test]
     fn get_vec_not_present() {
         let m: MultiMap<usize, usize> = MultiMap::new();
@@ -1140,6 +1148,14 @@ mod tests {
         assert_eq!(m.get_vec(&1), Some(&vec![5, 10]))
     }
 
+    #[test]
+    fn get_mut_empty() {
+        let mut m: MultiMap<usize, usize> = MultiMap::new();
+        m.insert(1, 42);
+        m.get_vec_mut(&1).and_then(Vec::pop);
+        assert_eq!(m.get_mut(&1), None);
+    }
+
     #[test]
     fn keys() {
         let mut m: MultiMap<usize, usize> = MultiMap::new();