From 7da4f8add9fcb58c320ef8a5a71305a0e78c8eae Mon Sep 17 00:00:00 2001
From: Revone <zrwusa@gmail.com>
Date: Sun, 26 Nov 2023 20:13:34 +0800
Subject: [PATCH] fix: In Graph data structures, only use 'undefined' and
 abandon the design where both 'null' and 'undefined' coexist.

---
 test/unit/data-structures/graph/abstract-graph.test.ts | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/test/unit/data-structures/graph/abstract-graph.test.ts b/test/unit/data-structures/graph/abstract-graph.test.ts
index 54b0ac0..dd2387b 100644
--- a/test/unit/data-structures/graph/abstract-graph.test.ts
+++ b/test/unit/data-structures/graph/abstract-graph.test.ts
@@ -36,11 +36,11 @@ class MyGraph<
     return new MyEdge(srcOrV1, destOrV2, weight, value) as EO;
   }
 
-  deleteEdge(edge: EO): EO | null {
+  deleteEdge(edge: EO): EO | undefined {
     return edge;
   }
 
-  getEdge(srcOrKey: VertexKey, destOrKey: VertexKey): EO | null {
+  getEdge(srcOrKey: VertexKey, destOrKey: VertexKey): EO | undefined {
     return new MyEdge(srcOrKey, destOrKey) as EO;
   }
 
@@ -62,8 +62,8 @@ class MyGraph<
     return [new MyVertex(a, 'b') as VO];
   }
 
-  getEndsOfEdge(edge: EO): [VO, VO] | null {
-    return edge ? null : null;
+  getEndsOfEdge(edge: EO): [VO, VO] | undefined {
+    return edge ? undefined : undefined;
   }
 
   protected _addEdgeOnly(edge: EO): boolean {