[HUDI-5206] RowColumnReader should not return null value for certain null child columns

[SteNicholas]

Change Logs

When reading to vector of certain null child columns of row type column, RowColumnReader should not return null value because the value of the row type column may not be null, which results in incorrect values of row type column.

Impact

The return value RowColumnReader#readToVector is correct for the row type column in the case that there are certain null child columns.

Risk level (write none, low medium or high below)

If medium or high, explain what verification was done to mitigate the risks.

Documentation Update

Describe any necessary documentation update if there is any new feature, config, or user-facing change

• The config description must be updated if new configs are added or the default value of the configs are changed
• Any new feature or user-facing change requires updating the Hudi website. Please create a Jira ticket, attach the
  ticket number here and follow the instruction to make
  changes to the website.

Contributor's checklist

• Read through contributor's guide
• Change Logs and Impact were stated clearly
• Adequate tests were added if applicable
• CI passed

[danny0405]

+1, looks good ~

[hudi-bot]

CI report:

• 3824274 Azure: FAILURE

Bot commands

@hudi-bot supports the following commands:

• @hudi-bot run azure re-run the last Azure build

[danny0405]

The added test has passed, would merge it soon ~