[MM-32734] Convert value to string to prevent crash (#5164) (#5171)

* Convert value to string

* Add default value prop

(cherry picked from commit ed4b100962)

Co-authored-by: Miguel Alatzar <migbot@users.noreply.github.com>

app/components/markdown/markdown.js

@@ -73,6 +73,7 @@ export default class Markdown extends PureComponent {
         disableChannelLink: false,
         disableAtChannelMentionHighlight: false,
         disableGallery: false,
+        value: '',
     };
 
     constructor(props) {
@@ -444,7 +445,7 @@ export default class Markdown extends PureComponent {
     };
 
     render() {
-        let ast = this.parser.parse(this.props.value);
+        let ast = this.parser.parse(this.props.value.toString());
 
         ast = combineTextNodes(ast);
         ast = addListItemIndices(ast);

app/components/markdown/markdown.test.js

@@ -44,4 +44,15 @@ describe('Markdown', () => {
             <Markdown {...props}/>,
         );
     });
+
+    test('should not crash when given a non-string value', () => {
+        const props = {
+            ...baseProps,
+            value: 10,
+        };
+
+        shallow(
+            <Markdown {...props}/>,
+        );
+    });
 });