fixed possible nil panic when item is deleted immediately after being added

cache.go

@@ -131,12 +131,20 @@ func (c *Cache) worker() {
 				c.gc()
 			}
 		case item := <-c.deletables:
-			c.list.Remove(item.element)
+			if item.element == nil {
+				item.promotions = -2
+			} else {
+				c.list.Remove(item.element)
+			}
 		}
 	}
 }
 
 func (c *Cache) doPromote(item *Item) bool {
+	//already deleted
+	if item.promotions == -2 {
+		return false
+	}
 	item.promotions = 0
 	if item.element != nil { //not a new item
 		c.list.MoveToFront(item.element)

cache_test.go

@@ -13,6 +13,15 @@ func Test_Cache(t *testing.T) {
 	Expectify(new(CacheTests), t)
 }
 
+func (c *CacheTests) DeletesAValue() {
+	cache := New(Configure())
+	cache.Set("spice", "flow", time.Minute)
+	cache.Set("worm", "sand", time.Minute)
+	cache.Delete("spice")
+	Expect(cache.Get("spice")).To.Equal(nil)
+	Expect(cache.Get("worm").(string)).To.Equal("sand")
+}
+
 func (c *CacheTests) GCsTheOldestItems() {
 	cache := New(Configure().ItemsToPrune(10))
 	for i := 0; i < 500; i++ {