Support empty body and only remove existing labels

[dokimiki]

In #34 it was improved to check if body is undefined, but in #57 it was changed to check if it is falsy.

https://docs.github.com/ja/webhooks-and-events/webhooks/webhook-events-and-payloads#issues
https://docs.github.com/ja/webhooks-and-events/webhooks/webhook-events-and-payloads#pull_request

It says if the body of an Issue is empty, it returns null, so when getting it, null is replaced with an empty character.

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Fixes #61

[dokimiki]

@stephanmiehe Is it possible to be reviewed or get an advice about this please?

[iba-1]

@dokimiki I just tried it on a private repo, some more code is actually needed as:

issue-labeler/src/main.ts

Lines 119 to 125 in 1fff18e

	function getIssueOrPRBody() {
	const { issue, pull_request } = context.payload;
	if (issue?.body === null || pull_request?.body === null) {
	return '';
	}
	return issue?.body ?? pull_request?.body;
	}

will return '' for an empty body, but '' is a falsy value and it'll be evaluated as false in this condition:

issue-labeler/src/main.ts

Lines 32 to 35 in 1fff18e

	if (!issue_body) {
	console.log("Could not get issue or PR body from context, exiting");
	return;
	}

therefore vanishing your intent of catching an empty body.

This could solve this problem, although is not very elegant:

 if (!issue_body && issue_body !== '' ) { 
   console.log("Could not get issue or PR body from context, exiting"); 
   return; 
 } 

[dokimiki]

@iba-1 thanks for testing my PR and founding bug!

To solve this problem, I have changed the method of evaluation, referring to your code, as follows:

issue-labeler/src/main.ts

Lines 31 to 35 in 2e0a8f2

	const issue_body = getIssueOrPRBody();
	if (issue_body === undefined) {
	console.log("Could not get issue or PR body from context, exiting");
	return;
	}

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[iba-1]

Thank you @stephanmiehe!