This improves the date and time number formats

- Now support applying date and time number format for 812 language tags
- Fix panic on getting merged cells with the same start and end axis

merge.go

@@ -289,5 +289,9 @@ func (m *MergeCell) GetStartAxis() string {
 // GetEndAxis returns the bottom right cell reference of merged range, for
 // example: "D4".
 func (m *MergeCell) GetEndAxis() string {
-	return strings.Split((*m)[0], ":")[1]
+	coordinates := strings.Split((*m)[0], ":")
+	if len(coordinates) == 2 {
+		return coordinates[1]
+	}
+	return coordinates[0]
 }

merge_test.go

@@ -80,6 +80,13 @@ func TestMergeCell(t *testing.T) {
 	assert.True(t, ok)
 	ws.(*xlsxWorksheet).MergeCells = &xlsxMergeCells{Cells: []*xlsxMergeCell{nil, nil}}
 	assert.NoError(t, f.MergeCell("Sheet1", "A2", "B3"))
+	// Test getting merged cells with the same start and end axis
+	ws.(*xlsxWorksheet).MergeCells = &xlsxMergeCells{Cells: []*xlsxMergeCell{{Ref: "A1"}}}
+	mergedCells, err := f.GetMergeCells("Sheet1")
+	assert.NoError(t, err)
+	assert.Equal(t, "A1", mergedCells[0].GetStartAxis())
+	assert.Equal(t, "A1", mergedCells[0].GetEndAxis())
+	assert.Empty(t, mergedCells[0].GetCellValue())
 }
 
 func TestMergeCellOverlap(t *testing.T) {