feat: support references-empty rule.(fix #17)

Author: hyiso

lib/src/ensure.dart

@@ -74,7 +74,7 @@ bool ensureEmpty(dynamic raw) {
   if (raw is String) {
     return raw.isEmpty;
   }
-  if (raw is Iterable<String>) {
+  if (raw is Iterable) {
     return raw.isEmpty;
   }
   return false;

lib/src/rules.dart

@@ -36,6 +36,7 @@ Map<String, RuleFunction> get supportedRules => {
       'footer-max-length': maxLengthRule(CommitComponent.footer),
       'footer-max-line-length': maxLineLengthRule(CommitComponent.footer),
       'footer-min-length': minLengthRule(CommitComponent.footer),
+      'references-empty': emptyRule(CommitComponent.references),
     };
 
 /// Build full stop rule for commit component.

lib/src/types/commit.dart

@@ -53,6 +53,8 @@ class Commit {
         return body as T?;
       case CommitComponent.footer:
         return footer as T?;
+      case CommitComponent.references:
+        return references as T?;
     }
   }
 }
@@ -64,6 +66,7 @@ enum CommitComponent {
   header,
   body,
   footer,
+  references,
 }
 
 /// Commit Note

test/lint_test.dart

@@ -92,6 +92,26 @@ void main() {
         throwsRangeError);
   });
 
+  test('succeds for issue', () async {
+    final result = await lint('somehting #1', {
+      'references-empty': Rule(
+        severity: RuleSeverity.error,
+        condition: RuleCondition.never,
+      ),
+    });
+    expect(result.valid, true);
+  });
+
+  test('fails for issue', () async {
+    final result = await lint('somehting #1', {
+      'references-empty': Rule(
+        severity: RuleSeverity.error,
+        condition: RuleCondition.always,
+      ),
+    });
+    expect(result.valid, false);
+  });
+
   test('positive on multi-line body message', () async {
     final message = '''chore(deps): bump commitlint_cli from 0.5.0 to 0.6.0
 Bumps [commitlint_cli](https://github.com/hyiso/commitlint) from 0.5.0 to 0.6.0.