fix broken what links here widget

src/public/app/entities/note_short.js

@@ -481,6 +481,17 @@ class NoteShort {
             .map(attributeId => this.treeCache.attributes[attributeId]);
     }
 
+    /**
+     * Get relations which target this note
+     *
+     * @returns {NoteShort[]}
+     */
+    async getTargetRelationSourceNotes() {
+        const targetRelations = this.getTargetRelations();
+
+        return await this.treeCache.getNotes(targetRelations.map(tr => tr.noteId));
+    }
+
     /**
      * Return note complement which is most importantly note's content
      *

src/public/app/services/tree_cache.js

@@ -141,7 +141,7 @@ class TreeCache {
 
             const note = this.notes[attributeRow.noteId];
 
-            if (!note.attributes.includes(attributeId)) {
+            if (note && !note.attributes.includes(attributeId)) {
                 note.attributes.push(attributeId);
             }
 

src/public/app/widgets/collapsible_widgets/what_links_here.js

@@ -53,4 +53,4 @@ export default class WhatLinksHereWidget extends CollapsibleWidget {
             this.refresh();
         }
     }
-}
+}

src/routes/api/tree.js

@@ -38,7 +38,8 @@ function getNotesAndBranchesAndAttributes(noteIds) {
             position,
             isInheritable
         FROM attributes
-        WHERE isDeleted = 0 AND noteId IN (???)`, noteIds);
+        WHERE isDeleted = 0 
+          AND (noteId IN (???) OR (type = 'relation' AND value IN (???)))`, noteIds);
 
     // sorting in memory is faster
     attributes.sort((a, b) => a.position - b.position < 0 ? -1 : 1);