Allow Connection Edit View to handle entries with NULL 'extra'

[XD-DENG]

closes: #12148 , a bug I observe in 2.0.0a2.

The root-cause is simple:
if the connection data is {..., "extra": None} (which is common), then form.data.get('extra', '{}') would return None rather than '{}', which causes error given json.loads() does not accept None.

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[potiuk]

That's cool. If possible to add a unit test, that would be great but it's ok like it is anyway

[github-actions]

The PR should be OK to be merged with just subset of tests as it does not modify Core of Airflow. The committers might merge it or can add a label 'full tests needed' and re-run it to run all tests if they see it is needed!

[ashb]

Could you add tests please?

[XD-DENG]

Thanks @potiuk and @ashb .

Have some arrangement later so will only be able to add the test either tonight or tomorrow. Will ping you then.

[github-actions]

The Workflow run is cancelling this PR. It has some failed jobs matching ^Pylint$,^Static checks,^Build docs$,^Spell check docs$,^Backport packages$,^Provider packages,^Checks: Helm tests$,^Test OpenAPI*.

[XD-DENG]

hi @potiuk @ashb @kaxil , simple test is added to ensure case where connection's extra is None can be handled.

Earlier I had another test case where connection has no extra field. But eventually I decided to remove it given this case may never happen if I'm not wrong

[XD-DENG]

It's the quarantined tests suite failing, and the main test cases are fine. So merging this now.