[MM 13934] Prevent blank mention keys from crashing the app (#2570)

* don’t match blank word boundaries

* test for blank mention keys

* Check for blank mention before looking for match

* account for multiple spaces as a blank mention

app/components/markdown/transform.js

@@ -310,11 +310,15 @@ export function getFirstMention(str, mentionKeys) {
     let firstMentionIndex = -1;
 
     for (const mention of mentionKeys) {
+        if (mention.key.trim() === '') {
+            continue;
+        }
+
         const flags = mention.caseSensitive ? '' : 'i';
         const pattern = new RegExp(`\\b${escapeRegex(mention.key)}_*\\b`, flags);
 
         const match = pattern.exec(str);
-        if (!match) {
+        if (!match || match[0] === '') {
             continue;
         }
 

app/components/markdown/transform.test.js

@@ -2758,6 +2758,11 @@ describe('Components.Markdown.transform', () => {
             input: 'apple banana orange',
             mentionKeys: [{key: '*\\3_.'}],
             expected: {index: -1, mention: null},
+        }, {
+            name: 'no blank mention keys',
+            input: 'apple banana orange',
+            mentionKeys: [{key: ''}],
+            expected: {index: -1, mention: null},
         }];
 
         for (const test of tests) {