Fix FOR XML RAW('') empty element name handling and all-NULL row outp…

[JapleenKaur3]

Description

Fix FOR XML RAW behavior with empty element name and all-NULL rows

Changes are in tsql_row_to_xml_raw() in forxml.c. When element_name is empty, the opening and closing wrapper tags are now skipped in ELEMENTS mode (same approach as PATH mode). For attribute-centric mode (without ELEMENTS), an error is raised since empty row tag names are not valid. The self-closing tag logic for all-NULL rows was also corrected.

Authored-by: Japleen Kaur amjj@amazon.com
Signed-off-by: Japleen Kaur amjj@amazon.com

Cherry-picked from - #4680

Issues Resolved

JIRA : BABEL-6379

1. FOR XML RAW(''), ELEMENTS — Babelfish produced <><a>1</a><b>2</b></> (invalid XML with empty wrapper tags). SQL Server produces <a>1</a><b>2</b> (no wrapper). Fixed by skipping the wrapper tag when element name is empty, consistent with how PATH('') handles it.

2. FOR XML RAW('') (without ELEMENTS) — Babelfish produced < a="1" b="2"/> (invalid XML). SQL Server throws: "Row tag omission (empty row tag name) cannot be used with attribute-centric FOR XML serialization." Fixed by adding the same error that PATH mode already throws for this case.

3. All-NULL rows with ELEMENTS — Babelfish produced <row></row>. SQL Server produces<row/> (self-closing tag). Fixed by replacing the closing > of the opening tag with /> when all columns are NULL.

Test Scenarios Covered

• Use case based -
  RAW(''), ELEMENTS without wrapper tag, RAW('') error without ELEMENTS, all-NULL rows producing .

• Boundary conditions -
  Empty element name (RAW('')).

• Arbitrary inputs -
  N/A

• Negative test cases -
  N/A

• Minor version upgrade tests -
  N/A

• Major version upgrade tests -
  N/A

• Performance tests -
  N/A

• Tooling impact -
  N/A

• Client tests -
  N/A

Check List

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