compose [nfc]: Simplify inlineLink by dropping null destination

Now that the caller is passing a string instead of a Uri object, the
caller that wants an empty string here can just pass an empty string.

Author: gnprice

lib/model/compose.dart

@@ -188,7 +188,7 @@ String wildcardMention(WildcardMentionOption wildcardOption, {
 /// result may be surprising.
 ///
 /// The part between "(" and ")" is just a "link destination" (no "link title").
-/// That destination is the string [destination], if provided.
+/// That destination is the string [destination].
 /// If [destination] has parentheses in it, the result may be surprising.
 // TODO: Try harder to guarantee output that creates an inline link,
 //   and in particular, the intended one. We could help with this by escaping
@@ -199,8 +199,8 @@ String wildcardMention(WildcardMentionOption wildcardOption, {
 //   > Backtick code spans, autolinks, and raw HTML tags bind more tightly
 //   > than the brackets in link text. Thus, for example, [foo`]` could not be
 //   > a link text, since the second ] is part of a code span.
-String inlineLink(String visibleText, String? destination) {
-  return '[$visibleText](${destination ?? ''})';
+String inlineLink(String visibleText, String destination) {
+  return '[$visibleText]($destination)';
 }
 
 /// What we show while fetching the target message's raw Markdown.

lib/widgets/compose_box.dart

@@ -350,7 +350,7 @@ class ComposeContentController extends ComposeController<ContentValidationError>
     final tag = _nextUploadTag;
     _nextUploadTag += 1;
     final linkText = zulipLocalizations.composeBoxUploadingFilename(filename);
-    final placeholder = inlineLink(linkText, null);
+    final placeholder = inlineLink(linkText, '');
     _uploads[tag] = (filename: filename, placeholder: placeholder);
     notifyListeners(); // _uploads change could affect validationErrors
     value = value.replaced(insertionIndex(), '$placeholder\n\n');

test/model/compose_test.dart

@@ -320,7 +320,7 @@ hello
 
   test('inlineLink', () {
     check(inlineLink('CZO', 'https://chat.zulip.org/')).equals('[CZO](https://chat.zulip.org/)');
-    check(inlineLink('Uploading file.txt…', null)).equals('[Uploading file.txt…]()');
+    check(inlineLink('Uploading file.txt…', '')).equals('[Uploading file.txt…]()');
     check(inlineLink('IMG_2488.png', '/user_uploads/2/a3/ucEMyjxk90mcNF0y9rmW5XKO/IMG_2488.png'))
       .equals('[IMG_2488.png](/user_uploads/2/a3/ucEMyjxk90mcNF0y9rmW5XKO/IMG_2488.png)');
   });