Comments: Avoid PHP notice in `get_comment_reply_link()` for `null` comment.

If there is no global comment, or the input comment is null, return early to prevent warnings.

Fixes #41846
Props birgire, earnjam



git-svn-id: https://develop.svn.wordpress.org/trunk@46335 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/comment-template.php

@@ -1646,6 +1646,10 @@ function get_comment_reply_link( $args = array(), $comment = null, $post = null
 
 	$comment = get_comment( $comment );
 
+	if ( empty( $comment ) ) {
+		return;
+	}
+
 	if ( empty( $post ) ) {
 		$post = $comment->comment_post_ID;
 	}

tests/phpunit/tests/comment/getCommentReplyLink.php

@@ -66,4 +66,24 @@ class Tests_Comment_GetCommentReplyLink extends WP_UnitTestCase {
 
 		$this->assertContains( $expected_url, $comment_reply_link );
 	}
+
+	/**
+	 * @ticket 41846
+	 */
+	public function test_should_return_null_when_depth_less_than_max_depth_and_comment_null_and_no_current_global_comment() {
+
+		// Let max depth be greater than depth and depth be non-zero.
+		$args = array(
+			'depth'     => 1,
+			'max_depth' => 2,
+		);
+
+		// Make sure there's no global comment object.
+		add_filter( 'get_comment', '__return_null' );
+
+		$actual = get_comment_reply_link( $args );
+
+		$this->assertNull( $actual );
+	}
+
 }