Change CollapsedTableBorders to handle empty nested table

Resolves: DEVSIX-1398

Autoported commit.
Original commit hash: [a26b6926d]

Author: joris.schellekens

itext.tests/itext.layout.tests/itext/layout/renderer/EmptyNestedTableTest.cs

@@ -0,0 +1,36 @@
+using System;
+using iText.Kernel.Pdf;
+using iText.Kernel.Utils;
+using iText.Layout;
+using iText.Layout.Element;
+using iText.Test;
+
+namespace iText.Layout.Renderer {
+    public class EmptyNestedTableTest : ExtendedITextTest {
+        public static readonly String sourceFolder = iText.Test.TestUtil.GetParentProjectDirectory(NUnit.Framework.TestContext
+            .CurrentContext.TestDirectory) + "/resources/itext/layout/EmptyNestedTableTest/";
+
+        public static readonly String destinationFolder = NUnit.Framework.TestContext.CurrentContext.TestDirectory
+             + "/test/itext/layout/EmptyNestedTableTest/";
+
+        /// <exception cref="System.IO.IOException"/>
+        /// <exception cref="System.Exception"/>
+        [NUnit.Framework.Test]
+        public virtual void BuildEmptyTable() {
+            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
+            NUnit.Framework.Assert.IsNull(new CompareTool().CompareByContent(outFileName, cmpFileName, destinationFolder
+                , "diff"));
+        }
+    }
+}

itext.tests/itext.layout.tests/resources/itext/layout/EmptyNestedTableTest/cmp_emptNestedTableTest.pdf

@@ -73,10 +73,10 @@ protected internal virtual iText.Layout.Renderer.CollapsedTableBorders CollapseA
             int[] rowspansToDeduct = new int[numberOfColumns];
             int numOfRowsToRemove = 0;
             for (int row = startRow - largeTableIndexOffset; row <= finishRow - largeTableIndexOffset; row++) {
-                currentRow = rows[row];
+                currentRow = rows.IsEmpty() ? null : rows[row];
                 bool 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];

itext/itext.layout/itext/layout/renderer/CollapsedTableBorders.cs

@@ -1 +1 @@
-07e073ffa9e240b2dc3aab3a5e221c71b6e3e9dd
+a26b6926d5a429dd4c61fb0fbdeee1855f337e94