[ZEPPELIN-6244] Handle Collection as defaultValue in GUI.select()

[renechoi]

[MINOR] Handle Collection as defaultValue in GUI.select()

What is this PR for?

This PR improves the GUI.select() method to properly handle Collection objects passed as defaultValue. When a Collection is provided, the method now extracts the first element as the actual default value instead of using the Collection object itself.

What type of PR is it?

Improvement

What is the Jira issue?

N/A (Minor improvement)

How should this be tested?

1. Run the test: ./mvnw test -pl zeppelin-interpreter -Dtest=GUITest
2. Verify that the new test testSelectWithCollectionDefault() passes
3. The test verifies that:
   • When a Collection containing ["2"] is passed as defaultValue
   • The select form uses "2" as the default value (not the Collection object)

Questions:

• Does the license files need update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No

Description

Problem

Currently, when using GUI.select() with a Collection as the defaultValue parameter, the entire Collection object is used as the default value. This can cause issues since the select form expects a single value, not a Collection.

Solution

Added logic to check if the defaultValue is a Collection (but not a String, since String implements CharSequence which is a Collection-like interface). If it is:

• Extract the first element from the Collection
• Use that element as the actual default value
• If the Collection is empty, use null

Code Changes

// Added to GUI.select() method
if (defaultValue instanceof Collection && !(defaultValue instanceof String)) {
  Collection<?> values = (Collection<?>) defaultValue;
  defaultValue = values.isEmpty() ? null : values.iterator().next();
}

Test Coverage

Added testSelectWithCollectionDefault() test that verifies:

• A Collection containing "2" is properly converted to default value "2"
• The form's default value is correctly set to "2"
• The selected value matches the expected default

This change improves the API's flexibility and prevents potential issues when Collections are inadvertently passed as default values.

[tbonelee]

Hello @renechoi , thank you for your contribution!

Since this PR slightly modifies the internal behavior of GUI.select(), it might be good to create a JIRA ticket to track this change. This helps us maintain consistency in the project and makes future reference easier.

[renechoi]

@tbonelee Thank you for the review! I've created a JIRA ticket as suggested: ZEPPELIN-6244

I'll update the PR title to include the JIRA issue number.

[Reamer]

@renechoi I do not see your announced test method testSelectWithCollectionDefault in the Change