Fixed an use case where the export of Excel failed if no students had answered it

src/pages/api/assignments/[id]/[export]/excel.ts

@@ -195,12 +195,16 @@ function commonExcel({
 
   // K10:M12 = 10,11,12,13
   // horizontally group Test Sections
+
+  // if there are test section headers to even merge:
+  if(testSectionHeaders.length > 1) {
     worksheet.mergeCells(
       startIndexTable,
       staticHeaders.length + 1,
       startIndexTable,
       tableColumnHeadersFirstPart.length
     );
+  }
 
   // Add the dynamic second and third header rows for test sections and sub-columns
   worksheet.addRow([