Fix MergeCells returning null for XLS files without merged cells#747
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XlsWorksheet only assigned MergeCells when the file contained merge cells, leaving it null for files with none. CsvWorksheet also returned null. XLSX and XLSB always return an empty array, so this was an inconsistency. Since null carries no extra meaning over an empty array, make all implementations consistent: always return an empty array. Calling AsDataSet with FillMergedCellsValue = true on files without merged cells (including all CSV files) previously threw ArgumentNullException. This fixes the crash.
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This was referenced Jun 16, 2026
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XlsWorksheet only assigned MergeCells when the file contained merge cells, leaving it null for files with none. CsvWorksheet also returned null. XLSX and XLSB always return an empty array, so this was an inconsistency.
Since null carries no extra meaning over an empty array, make all implementations consistent: always return an empty array.
Calling AsDataSet with FillMergedCellsValue = true on files without merged cells (including all CSV files) previously threw ArgumentNullException. This fixes the crash.