Fix undefined values appearing in CSS class names

[Copilot]

When optional fa-icon inputs (flip, rotate, pull, size) are undefined, they were generating class names like fa-undefined and fa-pull-undefined in the DOM.

Root Cause

The classlist generator used strict null checks (!== null) which don't filter undefined values:

• undefined !== null → true (class gets added)
• undefined != null → false (class filtered out)

Changes

• classlist.util.ts: Changed props.size !== null and props.pull !== null to use loose equality (!= null), consistent with existing checks for animation, rotate, and stackItemSize in the same file

• classlist.util.spec.ts: Added unit tests verifying undefined properties don't generate classes containing "undefined"

Before

[`fa-${props.size}`]: props.size !== null,  // undefined passes through
[`fa-pull-${props.pull}`]: props.pull !== null,  // undefined passes through

After

[`fa-${props.size}`]: props.size != null,  // undefined filtered
[`fa-pull-${props.pull}`]: props.pull != null,  // undefined filtered

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• accounts.google.com
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4238 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-77603855 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,1902122227314661081,7727019843955873751,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
  • Triggering command: /opt/google/chrome/chrome /usr/bin/google-chrome --user-data-dir=/tmp/karma-77603855 --enable-automation --no-default-browser-check --no-first-run --disable-default-apps --disable-popup-blocking --disable-translate --disable-REDACTED-timer-throttling --disable-renderer-REDACTEDing --disable-device-discovery-notifications --no-sandbox http://localhost:9876/?id=77603855 --headless --disable-gpu --disable-dev-shm-usage --remote-debugging-port=9222 (dns block)
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4408 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-63767769 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,3687498036657464119,170698497816152802,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
• clients2.google.com
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4238 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-77603855 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,1902122227314661081,7727019843955873751,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
  • Triggering command: /opt/google/chrome/chrome /usr/bin/google-chrome --user-data-dir=/tmp/karma-77603855 --enable-automation --no-default-browser-check --no-first-run --disable-default-apps --disable-popup-blocking --disable-translate --disable-REDACTED-timer-throttling --disable-renderer-REDACTEDing --disable-device-discovery-notifications --no-sandbox http://localhost:9876/?id=77603855 --headless --disable-gpu --disable-dev-shm-usage --remote-debugging-port=9222 (dns block)
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4408 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-63767769 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,3687498036657464119,170698497816152802,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
• clientservices.googleapis.com
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4238 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-77603855 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,1902122227314661081,7727019843955873751,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
  • Triggering command: /opt/google/chrome/chrome /usr/bin/google-chrome --user-data-dir=/tmp/karma-77603855 --enable-automation --no-default-browser-check --no-first-run --disable-default-apps --disable-popup-blocking --disable-translate --disable-REDACTED-timer-throttling --disable-renderer-REDACTEDing --disable-device-discovery-notifications --no-sandbox http://localhost:9876/?id=77603855 --headless --disable-gpu --disable-dev-shm-usage --remote-debugging-port=9222 (dns block)
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4408 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-63767769 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,3687498036657464119,170698497816152802,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
• googlechromelabs.github.io
  • Triggering command: /usr/local/bin/node /usr/local/bin/node install.js (dns block)
• redirector.gvt1.com
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4238 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-77603855 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,1902122227314661081,7727019843955873751,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
  • Triggering command: /opt/google/chrome/chrome /usr/bin/google-chrome --user-data-dir=/tmp/karma-77603855 --enable-automation --no-default-browser-check --no-first-run --disable-default-apps --disable-popup-blocking --disable-translate --disable-REDACTED-timer-throttling --disable-renderer-REDACTEDing --disable-device-discovery-notifications --no-sandbox http://localhost:9876/?id=77603855 --headless --disable-gpu --disable-dev-shm-usage --remote-debugging-port=9222 (dns block)
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4408 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-63767769 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,3687498036657464119,170698497816152802,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
• safebrowsingohttpgateway.googleapis.com
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4238 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-77603855 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,1902122227314661081,7727019843955873751,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
  • Triggering command: /opt/google/chrome/chrome /usr/bin/google-chrome --user-data-dir=/tmp/karma-77603855 --enable-automation --no-default-browser-check --no-first-run --disable-default-apps --disable-popup-blocking --disable-translate --disable-REDACTED-timer-throttling --disable-renderer-REDACTEDing --disable-device-discovery-notifications --no-sandbox http://localhost:9876/?id=77603855 --headless --disable-gpu --disable-dev-shm-usage --remote-debugging-port=9222 (dns block)
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4408 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-63767769 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,3687498036657464119,170698497816152802,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
• www.google.com
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4238 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-77603855 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,1902122227314661081,7727019843955873751,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
  • Triggering command: /opt/google/chrome/chrome /usr/bin/google-chrome --user-data-dir=/tmp/karma-77603855 --enable-automation --no-default-browser-check --no-first-run --disable-default-apps --disable-popup-blocking --disable-translate --disable-REDACTED-timer-throttling --disable-renderer-REDACTEDing --disable-device-discovery-notifications --no-sandbox http://localhost:9876/?id=77603855 --headless --disable-gpu --disable-dev-shm-usage --remote-debugging-port=9222 (dns block)
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --disable-dev-shm-usage --use-angle=swiftshader-webgl --crashpad-handler-pid=4408 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/karma-63767769 --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,3687498036657464119,170698497816152802,262144 --disable-features=PaintHolding --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Class names in DOM contain undefined</issue_title>
<issue_description>### Describe the problem
If we don't give an input to fa-icon, like flip or rotate, then we will have class names in the DOM like: svg-inline--fa fa-square-check fa-undefined fa-pull-undefined.

What did you expect?

I think, if an input is undefined, it shouldn't be added to the class name list.
I expect these classes in the DOM: svg-inline--fa fa-square-check

Reproducible test case

I can reproduce in the example on Github: StackBlitz Starter Sample

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Class names in DOM contain undefined #485

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.