Fix null handling, covered by integration tests

`core.getInput()` always returns a string, so testing for 'not null'
is always true. This then leads to previews set to an array with
a single empty string, breaking accept-header output.

Updated eslint rules should help avoid this issue in future, and new
integration tests verify that the github client configuration now
reflects the intended configuration options.

src/main.ts

@@ -7,10 +7,10 @@ import * as io from '@actions/io'
 import {requestLog} from '@octokit/plugin-request-log'
 import {retry} from '@octokit/plugin-retry'
 import {RequestRequestOptions} from '@octokit/types'
-import {callAsyncFunction} from './async-function'
-import {getRetryOptions, parseNumberArray, RetryOptions} from './retry-options'
-import {wrapRequire} from './wrap-require'
 import fetch from 'node-fetch'
+import {callAsyncFunction} from './async-function'
+import {RetryOptions, getRetryOptions, parseNumberArray} from './retry-options'
+import {wrapRequire} from './wrap-require'
 
 process.on('unhandledRejection', handleError)
 main().catch(handleError)
@@ -25,7 +25,7 @@ type Options = {
 
 async function main(): Promise<void> {
   const token = core.getInput('github-token', {required: true})
-  const debug = core.getInput('debug')
+  const debug = core.getBooleanInput('debug')
   const userAgent = core.getInput('user-agent')
   const previews = core.getInput('previews')
   const retries = parseInt(core.getInput('retries'))
@@ -38,12 +38,13 @@ async function main(): Promise<void> {
     defaultGitHubOptions
   )
 
-  const opts: Options = {}
-  if (debug === 'true') opts.log = console
-  if (userAgent != null) opts.userAgent = userAgent
-  if (previews != null) opts.previews = previews.split(',')
-  if (retryOpts) opts.retry = retryOpts
-  if (requestOpts) opts.request = requestOpts
+  const opts: Options = {
+    log: debug ? console : undefined,
+    userAgent: userAgent || undefined,
+    previews: previews ? previews.split(',') : undefined,
+    retry: retryOpts,
+    request: requestOpts
+  }
 
   const github = getOctokit(token, opts, retry, requestLog)
   const script = core.getInput('script', {required: true})

src/retry-options.ts

@@ -36,7 +36,7 @@ export function getRetryOptions(
     `GitHub client configured with: (retries: ${
       requestOptions.retries
     }, retry-exempt-status-code: ${
-      retryOptions?.doNotRetry ?? 'octokit default: [400, 401, 403, 404, 422]'
+      retryOptions.doNotRetry ?? 'octokit default: [400, 401, 403, 404, 422]'
     })`
   )