FED-2812 Catch MouseEvent.dataTransfer null exception

[aaronlademann-wf]

The Problem

In Dart SDK versions with null-safety enabled, the interop for MouseEvent.dataTransfer is non-nullable despite the JS spec for dataTransfer clearly indicating that it can be null.

This can cause the SDK to throw when a MouseEvent is manually constructed (e.g. in a test utility), and the dataTransfer getter is then accessed when running with sound_null_safety enabled:

Unexpected null value encountered in Dart web platform libraries.

More info about these native non-null assertions can be found here if you're really curious

The Solution

While we cannot fix the native MouseEvent.dataTransfer issue directly, we can monkey patch this flawed non-null assertion for the SyntheticMouseEvent.dataTransfer property that all of our consumer's UI / tests will be accessing as they migrate to null safety.

This PR adds an extension method that catches the Dart SDK's exception in a new safeDataTransfer getter, and updates the wrapNativeMouseEvent implementation to make SyntheticMouseEvent.dataTransfer access the new safeDataTransfer getter instead of the native MouseEvent.dataTransfer directly.

QA

1. Verify that the test added in this PR fails without the new extension method (See failing tests here: [NO MERGE] MouseEvent.dataTransfer null exception - test failure example #397)
2. Verify that the same test is passing in this PR.

[aviary-wf]

Security Insights

No security relevant content was detected by automated scans.

Action Items

• Review PR for security impact; comment "security review required" if needed or unsure
• Verify aviary.yaml coverage of security relevant code

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Questions or Comments? Reach out on Slack: #support-infosec.

[KealJones]

+1

[KealJones]

+10

[kealjones-wk]

+10

[aaronlademann-wf]

@Workiva/release-management-pp

[rmconsole-wf]

+1 from RM