PR: Allow null channels in file to not crash setup.

There is an edge case where having `channels` in an environment file
but an empty list, and `channels` missing from the GHA options/keys
returns an unhelpful error message:

`Error: Cannot read property 'join' of null`

I've setup an example here which runs through all the permutations of
`channels` keys being set, missing, and nulled:

https://github.com/Lnaden/ghatesting/runs/1538195898?check_suite_focus=true

This PR attempts to fix that by relaxing the strict equals in `setup.ts`
from

`if (condaConfig["channels"] === "" && channels !== undefined) {`

to

`if (condaConfig["channels"] === "" && channels != null) {`

which should allow `channels != null` to catch both `null` and
`undefined` for `channels`. I also attempted to add an example to the
GitHub Actions tests (Example 9) to test this edge case specifically.

A few comments to this PR:
* I'm not familiar with Typescript and building GHAs, so this might not be correct and I'm happy to make changes and take feedback.
* If you use an env file with an empty `channels` list with the `conda` client to create an environment, it works fine and just defaults to whatever the `conda` is configured to. In my example above, setting no channels in either the file or the GHA keys works fine and pulls from the `default` channel.
* This behavior admittedly is ambiguous, so if you would rather this edge case throw an error, I would like to request a better error message.

.github/workflows/example-9.yml

@@ -0,0 +1,39 @@
+name: "Example 9: Empty Channels in file dont crash setup"
+
+on:
+  pull_request:
+    branches:
+      - "*"
+  push:
+    branches:
+      - "master"
+  schedule:
+    # Note that cronjobs run on master/main by default
+    - cron: "0 0 * * *"
+
+jobs:
+  example-9:
+    # prevent cronjobs from running on forks
+    if:
+      (github.event_name == 'schedule' && github.repository ==
+      'conda-incubator/setup-miniconda') || (github.event_name != 'schedule')
+    name: Ex9 (${{ matrix.python-version }}, ${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: ["ubuntu-latest", "macos-latest", "windows-latest"]
+        python-version: ["3.7", "2.7"]
+    steps:
+      - uses: actions/checkout@v2
+      - uses: ./
+        id: setup-miniconda
+        continue-on-error: true
+        with:
+          auto-update-conda: true
+          python-version: ${{ matrix.python-version }}
+          environment-file: etc/example-empty-channels-environment.yml
+      - run: |
+          conda info
+          conda list
+          printenv | sort

dist/setup/index.js

@@ -22022,7 +22022,8 @@ function setupMiniconda(installerUrl, minicondaVersion, architecture, condaVersi
                 if (environmentFile) {
                     let channels;
                     channels = environmentYaml["channels"];
-                    if (condaConfig["channels"] === "" && channels !== undefined) {
+                    // Check if channels is undefined or null (empty list) in the file. != should catch both, !== will get only one
+                    if (condaConfig["channels"] === "" && channels != null) {
                         condaConfig["channels"] = channels.join(",");
                     }
                     else if (!environmentExplicit) {
@@ -29298,7 +29299,7 @@ module.exports = defaults;
 /* 771 */
 /***/ (function(module) {
 
-module.exports = {"_args":[["[email protected]","/Users/goanpeca/Dropbox (Personal)/develop/conda-incubator/setup-miniconda"]],"_from":"[email protected]","_id":"[email protected]","_inBundle":false,"_integrity":"sha512-0td5ijfUPuubwLUu0OBoe98gZj8C/AA+RW3v67GPlGOrvxWjZmBXiBCRU+I8VEiNyJzjth40POfHiz2RB3gImA==","_location":"/cheerio","_phantomChildren":{},"_requested":{"type":"version","registry":true,"raw":"[email protected]","name":"cheerio","escapedName":"cheerio","rawSpec":"1.0.0-rc.3","saveSpec":null,"fetchSpec":"1.0.0-rc.3"},"_requiredBy":["/get-hrefs"],"_resolved":"https://registry.npmjs.org/cheerio/-/cheerio-1.0.0-rc.3.tgz","_spec":"1.0.0-rc.3","_where":"/Users/goanpeca/Dropbox (Personal)/develop/conda-incubator/setup-miniconda","author":{"name":"Matt Mueller","email":"[email protected]","url":"mat.io"},"bugs":{"url":"https://github.com/cheeriojs/cheerio/issues"},"dependencies":{"css-select":"~1.2.0","dom-serializer":"~0.1.1","entities":"~1.1.1","htmlparser2":"^3.9.1","lodash":"^4.15.0","parse5":"^3.0.1"},"description":"Tiny, fast, and elegant implementation of core jQuery designed specifically for the server","devDependencies":{"benchmark":"^2.1.0","coveralls":"^2.11.9","expect.js":"~0.3.1","istanbul":"^0.4.3","jquery":"^3.0.0","jsdom":"^9.2.1","jshint":"^2.9.2","mocha":"^3.1.2","xyz":"~1.1.0"},"engines":{"node":">= 0.6"},"files":["index.js","lib"],"homepage":"https://github.com/cheeriojs/cheerio#readme","keywords":["htmlparser","jquery","selector","scraper","parser","html"],"license":"MIT","main":"./index.js","name":"cheerio","repository":{"type":"git","url":"git://github.com/cheeriojs/cheerio.git"},"scripts":{"test":"make test"},"version":"1.0.0-rc.3"};
+module.exports = {"name":"cheerio","version":"1.0.0-rc.3","description":"Tiny, fast, and elegant implementation of core jQuery designed specifically for the server","author":"Matt Mueller <[email protected]> (mat.io)","license":"MIT","keywords":["htmlparser","jquery","selector","scraper","parser","html"],"repository":{"type":"git","url":"git://github.com/cheeriojs/cheerio.git"},"main":"./index.js","files":["index.js","lib"],"engines":{"node":">= 0.6"},"dependencies":{"css-select":"~1.2.0","dom-serializer":"~0.1.1","entities":"~1.1.1","htmlparser2":"^3.9.1","lodash":"^4.15.0","parse5":"^3.0.1"},"devDependencies":{"benchmark":"^2.1.0","coveralls":"^2.11.9","expect.js":"~0.3.1","istanbul":"^0.4.3","jquery":"^3.0.0","jsdom":"^9.2.1","jshint":"^2.9.2","mocha":"^3.1.2","xyz":"~1.1.0"},"scripts":{"test":"make test"}};
 
 /***/ }),
 /* 772 */

etc/example-empty-channels-environment.yml

@@ -0,0 +1,7 @@
+name: empty-channels-environment
+
+channels:
+
+dependencies:
+  - black
+  - anaconda-client