Change CollapsedTableBorders to handle empty nested table

Resolves: DEVSIX-1398

Author: joris.schellekens

layout/src/main/java/com/itextpdf/layout/renderer/CollapsedTableBorders.java

@@ -74,10 +74,10 @@ protected CollapsedTableBorders collapseAllBordersAndEmptyRows() {
         int[] rowspansToDeduct = new int[numberOfColumns];
         int numOfRowsToRemove = 0;
         for (int row = startRow - largeTableIndexOffset; row <= finishRow - largeTableIndexOffset; row++) {
-            currentRow = rows.get(row);
+            currentRow = rows.isEmpty() ? null : rows.get(row);
             boolean hasCells = false;
             for (int col = 0; col < numberOfColumns; col++) {
-                if (null != currentRow[col]) {
+                if (null != currentRow && null != currentRow[col]) {
                     int colspan = (int) currentRow[col].getPropertyAsInteger(Property.COLSPAN);
                     if (rowspansToDeduct[col] > 0) {
                         int rowspan = (int) currentRow[col].getPropertyAsInteger(Property.ROWSPAN) - rowspansToDeduct[col];

layout/src/test/java/com/itextpdf/layout/renderer/EmptyNestedTableTest.java

@@ -0,0 +1,48 @@
+package com.itextpdf.layout.renderer;
+
+import com.itextpdf.kernel.pdf.PdfDocument;
+import com.itextpdf.kernel.pdf.PdfWriter;
+import com.itextpdf.kernel.utils.CompareTool;
+import com.itextpdf.layout.Document;
+import com.itextpdf.layout.element.Cell;
+import com.itextpdf.layout.element.Table;
+import com.itextpdf.test.ExtendedITextTest;
+import com.itextpdf.test.annotations.type.IntegrationTest;
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+import java.io.File;
+import java.io.IOException;
+
+/**
+ */
+@Category(IntegrationTest.class)
+public class EmptyNestedTableTest extends ExtendedITextTest {
+
+    public static final String sourceFolder = "./src/test/resources/com/itextpdf/layout/EmptyNestedTableTest/";
+    public static final String destinationFolder = "./target/test/com/itextpdf/layout/EmptyNestedTableTest/";
+
+    @Test
+    public void buildEmptyTable() throws IOException, InterruptedException {
+
+        String outFileName = destinationFolder + "emptNestedTableTest.pdf";
+        String cmpFileName = sourceFolder + "cmp_emptNestedTableTest.pdf";
+
+        // setup document
+        PdfDocument pdfDocument = new PdfDocument(new PdfWriter(outFileName));
+        pdfDocument.setTagged();
+        Document layoutDocument = new Document(pdfDocument);
+
+        // add table to document
+        Table x = new Table(1).addCell(new Cell().add(new Table(1)));
+        layoutDocument.add(x);
+
+        // close document
+        layoutDocument.close();
+
+        // compare
+        Assert.assertNull(new CompareTool().compareByContent(outFileName, cmpFileName, destinationFolder, "diff"));
+    }
+
+}