Fix type issues

src/utils/LruCache.ts

@@ -93,7 +93,7 @@ export class LruCache<K, V> {
             return;
         }
 
-        const newItem = {
+        const newItem: CacheItem<K, V> = {
             key,
             value,
             next: null,
@@ -120,7 +120,10 @@ export class LruCache<K, V> {
             // Map size exceeded cache capcity. Drop tail item.
             this.map.delete(this.tail.key);
             this.tail = this.tail.prev;
-            this.tail.next = null;
+
+            if (this.tail) {
+                this.tail.next = null;
+            }
         }
     }
 
@@ -159,8 +162,13 @@ export class LruCache<K, V> {
         if (item === this.head) return item;
 
         this.removeItemFromList(item);
-        // …and put it to the front.
-        this.head.prev = item;
+
+        // Put item to the front.
+
+        if (this.head) {
+            this.head.prev = item;
+        }
+
         item.prev = null;
         item.next = this.head;
         this.head = item;