add test

src/main/java/com/github/pjfanning/xlsx/impl/StreamingSheet.java

@@ -159,9 +159,13 @@ public Comment getCellComment(CellAddress cellAddress) {
   /**
    * Only works after sheet is fully read (because merged regions data is stored
    * at the end of the sheet XML).
+   *
+   * @param index the index of the merged region to retrieve
+   * @return the merged region at the specified index
+   * @throws NoSuchElementException if the index argument is not a valid index
    */
   @Override
-  public CellRangeAddress getMergedRegion(int index) {
+  public CellRangeAddress getMergedRegion(int index) throws NoSuchElementException {
     List<CellRangeAddress> regions = getMergedRegions();
     if(index > regions.size()) {
       throw new NoSuchElementException("index " + index + " is out of range");
@@ -217,7 +221,7 @@ public Hyperlink getHyperlink(int row, int column) {
    * This should only be called after all the rows are read because the hyperlink data is
    * at the end of the sheet.
    *
-   * @param cellAddress
+   * @param cellAddress the location of the cell
    * @return the hyperlink associated with this cell (only if feature is enabled on the Builder) - null if not found
    * @throws IllegalStateException if {@link com.github.pjfanning.xlsx.StreamingReader.Builder#setReadHyperlinks(boolean)} is not set to true
    */

src/main/java/com/github/pjfanning/xlsx/impl/StreamingWorkbook.java

@@ -70,7 +70,10 @@ public String getSheetName(int sheet) {
   }
 
   /**
-   * {@inheritDoc}
+   * Returns the index of the sheet by his name (case insensitive match)
+   *
+   * @param name the sheet name
+   * @return index of the sheet (0 based) or {@code -1} if not found
    */
   @Override
   public int getSheetIndex(String name) {
@@ -81,7 +84,7 @@ public int getSheetIndex(String name) {
    * Returns the index of the given sheet
    *
    * @param sheet the sheet to look up
-   * @return index of the sheet (0 based)
+   * @return index of the sheet (0 based) or {@code -1} if not found
    * @throws IllegalArgumentException if the sheet provided is not a StreamingSheet
    */
   @Override

src/test/java/com/github/pjfanning/xlsx/StreamingSheetTest.java

@@ -75,6 +75,16 @@ public void testMissingSheet() throws Exception {
     }
   }
 
+  @Test
+  public void testSheetIndexForMissingSheet() throws Exception {
+    try(
+            InputStream is = getInputStream("empty_sheet.xlsx");
+            Workbook workbook = StreamingReader.builder().open(is)
+    ) {
+      assertEquals(-1, workbook.getSheetIndex("non-existent"));
+    }
+  }
+
   @Test
   public void testEmptyCellShouldHaveGeneralStyle() throws Exception {
     try(