fix: commentBody may be null (#706)

* fix: `commentBody` may be `null`

This handles the cases where `pull_request_review` events have no
comments (`commentBody` field is `null`). In those cases, the `null`
value is converted to the empty string.

The issue was testing `!commentBody` which was triggerring on empty
strings as well. This guard was removed (which is the fix), but for
clarity, the `commentBody` field was also made optional to make it clear
that the comment may be missing.

* fix: bun run format

test/prepare-context.test.ts

@@ -10,6 +10,7 @@ import {
   mockPullRequestCommentContext,
   mockPullRequestReviewContext,
   mockPullRequestReviewCommentContext,
+  mockPullRequestReviewWithoutCommentContext,
 } from "./mockContext";
 
 const BASE_ENV = {
@@ -126,6 +127,24 @@ describe("parseEnvVarsWithContext", () => {
     });
   });
 
+  describe("pull_request_review event without comment", () => {
+    test("should parse pull_request_review event correctly", () => {
+      process.env = BASE_ENV;
+      const result = prepareContext(
+        mockPullRequestReviewWithoutCommentContext,
+        "12345",
+      );
+
+      expect(result.eventData.eventName).toBe("pull_request_review");
+      expect(result.eventData.isPR).toBe(true);
+      expect(result.triggerUsername).toBe("senior-developer");
+      if (result.eventData.eventName === "pull_request_review") {
+        expect(result.eventData.prNumber).toBe("321");
+        expect(result.eventData.commentBody).toBe("");
+      }
+    });
+  });
+
   describe("pull_request_review_comment event", () => {
     test("should parse pull_request_review_comment event correctly", () => {
       process.env = BASE_ENV;