fix an NPE when we encounter a package without a changelog (#50)

pkgs/firehose/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.3.10
+
+- Fixed an exception that occurred when no CHANGELOG.md file was present.
+
 ## 0.3.9
 
 - Update the 'publishable' PR comment to use a markdown table.

pkgs/firehose/lib/src/changelog.dart

@@ -24,6 +24,8 @@ class Changelog {
   }
 
   Iterable<_Section> _parseSections() sync* {
+    if (!exists) return;
+
     _Section? section;
 
     for (var line in file.readAsLinesSync().where((line) => line.isNotEmpty)) {

pkgs/firehose/pubspec.yaml

@@ -1,6 +1,6 @@
 name: firehose
 description: A tool to automate publishing of Pub packages from GitHub actions.
-version: 0.3.9
+version: 0.3.10
 repository: https://github.com/dart-lang/ecosystem/tree/main/pkgs/firehose
 
 environment:

pkgs/firehose/test/changelog_test.dart

@@ -37,6 +37,13 @@ void main() {
       });
     });
 
+    test('no changelog file', () {
+      var changelog = Changelog(File('missing_changelog.md'));
+      expect(changelog.exists, false);
+      expect(changelog.latestVersion, isNull);
+      expect(changelog.latestChangeEntries, isEmpty);
+    });
+
     test('latestChangeEntries', () {
       withChangelog(_defaultContents, (file) {
         var changelog = Changelog(file);