[BUG] NULL Columns passed as VARCHAR to Calcite, ResultSetMetadata for queries reports NULL columns as VARCHAR

[birschick-bq]

Environment

• DocumentDB JDBC driver version: 1.4.4
• DocumentDB server version: n/a
• OS: [e.g. MacOS Big Sur 11.5.1, Windows 10 64-bit]: n/a
• BI Tool or client name: n/a
• BI Tool or client version: n/a
• Java version (if known): n/a

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Problem Description

1. Steps to reproduce:
   • For SELECT fieldNull where DatabaseMetaData would report fieldNull as NULL, ResultSetMetadata is reporting the same field as VARCHAR when used in a query.
2. Expected behaviour:
   • column metadata should report NULL
3. Actual behaviour:
   • column metadata should report VARCHAR
4. Error message/stack trace:
5. Any other details that can be helpful:

• Test that changing the mapping here does not break existing tests.
• Test possible effects on cached query results in BI Tools (mainly target Tableau) if we add this fix.
• Confirm that NULL over VARCHAR is the right behaviour for this case.

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Screenshots

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JDBC log

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