Source

File: wp-includes/rest-api/endpoints/class-wp-rest-comments-controller.php

protected function get_comment( $id ) {
		$error = new WP_Error(
			'rest_comment_invalid_id',
			__( 'Invalid comment ID.' ),
			array( 'status' => 404 )
		);

		if ( (int) $id <= 0 ) {
			return $error;
		}

		$id      = (int) $id;
		$comment = get_comment( $id );
		if ( empty( $comment ) ) {
			return $error;
		}

		if ( ! empty( $comment->comment_post_ID ) ) {
			$post = get_post( (int) $comment->comment_post_ID );

			if ( empty( $post ) ) {
				return new WP_Error(
					'rest_post_invalid_id',
					__( 'Invalid post ID.' ),
					array( 'status' => 404 )
				);
			}
		}

		return $comment;
	}