From 1153ce43c6c2af45031a4a3dbaedc37d6a408241 Mon Sep 17 00:00:00 2001
From: Matthew Hodgson <matthew@matrix.org>
Date: Wed, 3 Apr 2019 20:38:25 +0100
Subject: [PATCH 1/3] fix NPE for rooms with redacted tombstones

---
 src/matrix-to.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/matrix-to.js b/src/matrix-to.js
index 15979000c4..99a02dc42d 100644
--- a/src/matrix-to.js
+++ b/src/matrix-to.js
@@ -241,7 +241,7 @@ export function makeRoomPermalink(roomId) {
 
     // If the roomId isn't actually a room ID, don't try to list the servers.
     // Aliases are already routable, and don't need extra information.
-    if (roomId[0] !== '!') return permalinkBase;
+    if (!roomId || roomId[0] !== '!') return permalinkBase;
 
     const client = MatrixClientPeg.get();
     const room = client.getRoom(roomId);

From e98ef0d5370c31819baa4ef3b57d1bc3b60acbc2 Mon Sep 17 00:00:00 2001
From: Matthew Hodgson <matthew@matrix.org>
Date: Wed, 3 Apr 2019 21:12:36 +0100
Subject: [PATCH 2/3] only show continues link if tombstone has a continuation

---
 src/components/views/rooms/MessageComposer.js | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/components/views/rooms/MessageComposer.js b/src/components/views/rooms/MessageComposer.js
index 535d565d22..576f45a3bc 100644
--- a/src/components/views/rooms/MessageComposer.js
+++ b/src/components/views/rooms/MessageComposer.js
@@ -362,18 +362,22 @@ export default class MessageComposer extends React.Component {
         } else if (this.state.tombstone) {
             const replacementRoomId = this.state.tombstone.getContent()['replacement_room'];
 
+            const continuesLink = replacementRoomId ? (
+                <a href={makeRoomPermalink(replacementRoomId)}
+                    className="mx_MessageComposer_roomReplaced_link"
+                    onClick={this._onTombstoneClick}
+                >
+                    {_t("The conversation continues here.")}
+                </a>
+            ) : '';
+
             controls.push(<div className="mx_MessageComposer_replaced_wrapper">
                 <div className="mx_MessageComposer_replaced_valign">
                     <img className="mx_MessageComposer_roomReplaced_icon" src={require("../../../../res/img/room_replaced.svg")} />
                     <span className="mx_MessageComposer_roomReplaced_header">
                         {_t("This room has been replaced and is no longer active.")}
                     </span><br />
-                    <a href={makeRoomPermalink(replacementRoomId)}
-                        className="mx_MessageComposer_roomReplaced_link"
-                        onClick={this._onTombstoneClick}
-                    >
-                        {_t("The conversation continues here.")}
-                    </a>
+                    { continuesLink }
                 </div>
             </div>);
         } else {

From b9eebee13be0b87788c32070e39248316a5e6e38 Mon Sep 17 00:00:00 2001
From: Matthew Hodgson <matthew@matrix.org>
Date: Thu, 4 Apr 2019 16:53:17 +0100
Subject: [PATCH 3/3] turn NPE into a throw

---
 src/matrix-to.js | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/matrix-to.js b/src/matrix-to.js
index 99a02dc42d..7223f2e33d 100644
--- a/src/matrix-to.js
+++ b/src/matrix-to.js
@@ -239,9 +239,13 @@ export function makeUserPermalink(userId) {
 export function makeRoomPermalink(roomId) {
     const permalinkBase = `${baseUrl}/#/${roomId}`;
 
+    if (!roomId) {
+        throw new Error("can't permalink a falsey roomId");
+    }
+
     // If the roomId isn't actually a room ID, don't try to list the servers.
     // Aliases are already routable, and don't need extra information.
-    if (!roomId || roomId[0] !== '!') return permalinkBase;
+    if (roomId[0] !== '!') return permalinkBase;
 
     const client = MatrixClientPeg.get();
     const room = client.getRoom(roomId);